Probably an unintentional mistake rather than a concious design decision. I think they used a transparent background instead of white, so it accidentally looks evil in night mode. To test, switch your phone out of night mode and see if it schanges the face to white along with the background.
Is it a translucent PNG? Because GIF doesn’t support alpha channels. Also why would they want their logo to shift color? Brand colors are super important
Ha! No, not anymore, not in the current design environment.
Literally every site and app is doing this exact same shit, in almost exactly the same way. They're tripping over themselves to strip away any identity or interesting design elements, and turn into another carbon copy of every other app's floaty, bubbly, needlessly vacant and boringly white/black design.