I've honestly never heard of Tildes til this post. As far as I can tell since there's no API he's just scraping html which is not ideal, but still it's worth checking out. I love that developers are still determined to make 3rd party apps.
If you know some Java, you may try to look into it with Jadx. It's a Java decompiler with Android support, and can also export code an Android Studio project if you don't like the built-in code viewer. It's on GitHub.
That seems like a pretty bad platform to develop an app for then lol at least APIs try to maintain backwards-compatibility (and give you only the data you need in an easier format), I can't imagine that being sustainable long-term.