I understand your point.
I see two explanations, on the one hand, it may be that the search engine automatically activates the search for content marked for adults under certain keywords, such as "NSFW" and not for others, such as "sex".
The second is that it is a mistake.
Either way, the person who has the last word is the administrator, without offending the excellent work that @no time for play does, but he is a moderator and from what I have read, he does not work or make decisions regarding the itch functioning
Keep in mind that if I search for a name, I'm not necessarily looking for adult games, that is, the engine has no way of knowing it, because in itch there are many games with similar or repeated names.
On the other hand, if you search for NSFW, you are actively looking for adult content.