Kinda seems spammy because it makes it look like this is something official. It uses the Android developers social header image, it uses the same
dev-challenge_hero-asset.svg
as the official compose challenge, and the may challenge image isn't even hosted by you, you're completely taking it from
<https://android-developers.googleblog.com/2021/03/android-dev-challenge-4.html>
Also, the fact that the prize is $100 in BTC adds to the spam/scammyness nature of it.
Also, it's a may challenge, but May is half-way through? I'd tread carefully on anyone moving forward with this. Looks like you might just be doing free work for somebody.
Edit:
Searching twitter for
composechallenge.com shows 0 results.
I will add that I will personally give this the benefit of the doubt and maybe it's actually made in good faith, but it takes/steals a lot of things from the official compose challenge and there doesn't seem to be any real organization behind this.