No, I don't believe we can say that there is autofill of form fields. The reason is that the page title is "Edit Your Details" indicating that the browser page being displayed is being intentionally created from the logged in user's profile. And the WARNING is not there, as well. So, the browser doesn't think it's on the page that matches the URL with form fields filled in automatically; it thinks it's on the profile of the logged in user (Super User).
When we just view a user's profile, the URL is displayed as: .../artist-profiles/###-<username> (we have a main menu item called "artist-profiles"). [### represents user ID]
When we click on Update User Profile, the URL is displayed as: .../cb-profile-edit/userdetails/###-<username>, but the profile being displayed is that of the logged in Super User, not the correct one that corresponds to the ID and username. And it is titled "Edit Your Details".
If we go to our own profile intentionally while logged in, the URL is displayed as: .../cb-profile-edit/userdetails (without any further identifying information like ID or username). The page is titled "Edit Your Details".
The only other thing of note is that, on the Joomla 3 live site, we do use an Extension called ProfileURL, which provides a shorter URL for profiles (such as <site>/<username of choice>). That Extension has not been updated to Joomla 4 compatibility so, at present, our Joomla 4 test installation has that Extension (all 5 elements) all disabled.