You are saying that you expected an authentic traditional roguelike experience from a developer who, by your own account doesn't even know what a roguelike is. What seems to have happened here is that the developer did not like what they were making, so they made something else instead. You seem to be suggesting that the reason this happened is that language is insufficiently prescriptivist, and not that the developer just saw something they liked better and changed their mind.
He did have a general idea of what could be construed as a Roguelike because the game he was creating at the time ticked most of the boxes for what a Roguelike should be like. The issue was that his game was directionless, he added features, then removed them, then added other features that did not really fit the game... The best way I can put it is that he designed it the same way I designed my first game ever and that game is not online, I am not proud of it.
And, I am certain it was caused by a term that was not prescriptive enough because ideas, opinions and ways of working are socially constructed and inspired. The person who made Pokemon created his game based on his childhood. Chain chomps from Super Mario Bros were born from a childhood trauma. When you find two artists online with a similar artstyle that is because one was inspired by the other. Inherently, everything you do, think and believe in were influenced by other people who, likewise, had their opinions influenced by other people or events.
Another point I would like to add is that if he had changed his mind he would have noted it directly in the video. If I made something I did not like no matter what I would tell people "I do not like making games of this genre, I will try to build something else that is more of my style", but in the video he still calls his finished product a Roguelike. So, the original idea was to make a Roguelike, his final idea was still to make a Roguelike, he did not have a change of mind in this regard. The only change of mind, maybe, was that he dropped the puzzle aspect of his game which is something he mentioned early in the video, but something that he did not follow through.
I don't see why that would be the case. Not all dungeon crawlers are roguelikes, not even close; and roguelites are probably almost as apt to be labeled dungeon crawlers as roguelikes are, given that dungeon crawling is typically considered a theme, not a genre. I decided to try this out for myself. Both The Binding of Isaac and Slay the Spire, which you keep bringing up as undesirable, are tagged "dungeon crawler" on Steam; in fact, when I browse the dungeon crawler tag on Steam, both of those games are prominently displayed in the banner at the top of the page. Glancing over the actual recommendations, I see a handful of traditional roguelikes, as is expected, but I mostly see other genres. If I were actually looking for roguelikes in this list, I would probably be disappointed. The roguelike list is, as you say, a mix of roguelikes and roguelites, but it looks more promising than the dungeon crawlers
I hardly use the tags directly when searching for games on Steam, I use the search bar which leads me to games tagged "Dungeon-Crawler" or "Roguelike", similarly to how any other social media site works. I should have been less vague when describing my issue, sorry. I found 4 Roguelikes that I would have otherwise not found, using "Dungeon Crawler" as a search word, but admittedly it is not that much better I have to dig deep just to find what I want with either keyword. I still believe that Dungeon-Crawler was marginally better, however, I don't know how much tags differ from the search bar, but I will try to use them more often if that means I have a higher chance to find what I want.
For the record, Slay The Spire is not really undesirable. I am somewhat intrigued by the game itself, but it is annoying to see it show up whenever I am searching for something else.
By the way, I know of folks who would take umbrage at grouping traditional roguelikes in with dungeon crawlers. To them, dungeon crawler is a term with a very specific, long-established meaning (which does not include Rogue) that has been diluted into uselessness, making it difficult to find the true dungeon crawlers amongst all the mislabeled pretenders.
Why would they? Didn't you say it was a theme, not a genre? A game that is not a Roguelike that I consider (To an extent) a Dungeon-Crawler is Zelda since you do exactly that, you crawl through dungeons, find the chests, find the keys and open doors, and I say 'to an extent' because that is only applicable to the dungeon themselves. Zelda has always been an action RPG/adventure game at heart, therefore, I would not call it a Dungeon-Crawler, I would call it an adventure game to remain as accurate as possible.
I am actually curious now, what do these people consider a game to be a dungeon-crawler? Perhaps it is something I'd like to play too.