You answer is not valid for a direct link. Nor is it correct for the games displayed on a creator/profile page. I believe you have misread the question. What you describe happens for the search & browse system - like itch.io itself.
A direct link to a game or the profile/creator page does not care for the logged in status. On games, there will be the age check warning.
But that age check warning does not appear on some creator pages and it will not appear on the profile page.
So, yes, clicking on https://lonely-visual.itch.io/ will show all projects, including the nsfw projects. And OP's creator page is one of the pages that do not have the age check, for whatever reason. The games do have the age check, so they are properly set up as nsfw. I actually think, that's a bug or oversight in the design of that age check system. It should appear even for https://itch.io/profile/lonely-visual - which is does not, not even for the developers where the age check appears for the creator page (the devname.itch.io page).