Like boxing will also match box. But it does not match any game that has no "box" in the title.
This is probably just search APIs auto-correcting and doing combined searches. This is a nice feature since boxing is also the gerund for the verb to box.
So why was the tag boxing not shown as a search result? Because it is not in the list of featured tags. Or suggested tags. Whatever you want to call them.
As I mentioned in my post from what I can test it's because tags used on a number below 200-300 games will not be autocompleted. "Boxing" has 165 games while "fishing" has 1,624 games. I am assuming that range as the cutting of point because the lowest tag to auto-complete I could figure out was "tennis" at 385 games.
I believe that people think this, but can you give an example, where the title has not resemblance to a word, yet you can find it in search? Fishing and Boxing were both negative.
Searching for "slugfest" will give you 4 games with slugfest on the title ahead of Toe II Toe and Super Slav Brothers. Those last two do not have the word "slugfest" in the title but do in the tagline and this ordering, title first, tagline later, seems to be by design.
I strongly believe that because my latest game is a stronger example of this. I am an NSFW dev and have been keeping all the info on this discussion SFW to avoid people giving me shit. But if you search for "giantess" (a common keyword for a kink) you will get first about 14 games that have the word in the title. Past that point, all the other games(about 24 more) do not feature the word in the title but do in the tagline. Btw, 3 games out of the 14 are doing the "Game title(Tag Tag Tag)" thing. Although one is not doing with the searched word but some other tags.