Have you considered that the guy who wrote that app is Russian, and that there (as well as in other places — like sub-Saharan Africa) blackface wasn’t a thing?
Racist caricatures, of course, are a thing all over the world. But Yaroslav Goncharov probably thought that this wouldn’t be a problem since it’s not caricatures — it’s trained on actual faces with the goal of being as realistic as possible.
The US (and to an only slightly lesser degree the rest of the Anglosphere, thanks to cultural osmosis) is uniquely touchy about caricature. If you look at comics, in the US realistic comics like superhero comics dominate. In Europe nonrealistic, caricatured styles dominate — think Asterix. I think the reason is that to use a caricatured style in the US, you would also have to caricature non-whites, and that’s just too dangerous. As a consequence, mainland European comics with few exceptions never made it big in the US, or anywhere in the Anglosphere. Americans are unused to the caricatured style, find it odd and childish and potentially offensive.
But publishers usually are aware and won’t let it go that far. You find many comics, popular all over the world, which are translated to twenty languages, but English isn’t one of them! (If they are in English as well, the market is often India).
Of course, you’re not wrong for being offended. It’s your culture, in your culture it’s seen as terribly rude and offensive, and thus where you are the people who still do it are usually dicks who intend to be rude and offensive.
But there are still probably some 5 billion people out there, of all complexions, who would be fascinated and amused by this app instead of offended. It’s a bit sad that you convinced the guy to take it down. Cultural norms in the US could be respected by Americans just not using the app for that, and not publishing or sharing race-swapped images (something, I note, all the news outlets outraged at the app did).