Seems a bit petty to me. As a developer I empathize with the possible lack of documentation (I don’t know, I never tried to integrate Sign In with Apple) but as a user I actually am super happy with it. Nowadays any iOS app that doesn’t support logging in with Apple makes me think twice about whether I really need the app.
The part where the developer puts the word 'privacy' in scare quotes is a bit of a red flag for me. Suggesting that "accept[ing] two "social logins": Google and Facebook. All was well." does not fill me with confidence that the developer respects privacy concerns.