> ASCII with rounded corners

To be that guy for a moment: those are not ASCII as those characters are not in the standard 7-bit ASCII set. The closest you get to rounded corners with just ASCII is something like:

    /-----\       .-----. 
    | bah |  or   | bah |   (the latter usually looks best IMO, but that can depend on font)
    \-----/       `-----' 

You'd get away with calling the linked diagram ANSI. While that is technically incorrect most people accept the term for something that uses one of the common 8-bit character sets that include those box-drawing characters (CP437, CP850, ISO-8859, Win1252, …), because that is what MS has for a long time called Win1252 in its tools.

> is already a red flag

I wouldn't call using box-drawing characters a red flag, I've known people use them this way for years and do so myself. The LLM generates them because they were in its training data because people use them. It might be something to consider amongst other flags but I don't consider it a strong signal on its own. The red flag for me is the alignment - if you are going to have your documentation ghostwritten at least make the effort to do a cursory editing pass afterwards.