> Wikipedia's asshole lawyers didn't like that I used a serifed W in the logo
It’s not the lawyers which don’t like it. Trademark exists to protect consumer confusion. If a reasonable person could reasonably (but incorrectly) believe that your app was officially associated with Wikipedia based on only looking at the logo, then you have created consumer confusion. Trademark law disallows you from (using trademarked branding) letting people believe that your app is official.
> I made it clear it wasn't an official Wikipedia product everywhere
Posting “No copyright infringement intended” on a YouTube video does not, contrary to masses of people, turn a copyright infringement into something else.
Likewise, just writing that your app is not official will not make a trademark infringement vanish.
(Of course, if Wikipedia does not have a valid trademark which you infringed, that’s another story. But it’s not what I would guess has happened here.)