If a dev does adult and family content, those should be put on different accounts, yes. In this case however, that is only sexy stuff. It is definitly not family content. It would not be considered 18+ by most official rating standard, but nsfw is such a vague term.
Oh, and Itch will consider a developer account as nsfw, once there are nsfw games on it. So the account cannot be found in search&browse.
The flaw goes even deeper. It has nothing to do with going to the nsfw game via the creator's page that you found with a sfw game. Once you are logged in and click a direct link to a nsfw game, the dialogue box will not appear, asking if you are 18+. (Or maybe it appeared the very first time, and this particular setting was saved to my account). I still can filter out adult content, but only from search and browse. And only if I do not use one of the adult tags. Like "adult". If you filter for tag adult, you will see nsfw results, even if you checked the box to not see such content in search & browse or are not logged in at all (just use a private tab for testing).
All this is not very intuitive and Itch should rework their maturity settings. Or rather implement some. It would also help all those players complaining about horror games. There is more to "nsfw" than sexy stuff. A lot of those horror games are not suitable for kids, yet will not be marked as adult content.