Yet another click-bait headline - on the verge of outright misrepresentation.
The tweet in question (https://twitter.com/houseparty/status/1244827034406121472) clearly offers the bounty for "the first individual to provide proof [that the recent hacking rumors were spread by a paid commercial smear campaign to harm Houseparty]". The article goes to great lengths to explain this is exactly what didn't happen and so no bounty makes sense.
Edit: I just noticed the headline of the article is actually more correct. Maybe someone can fix the title on this post. As I write this comment, the title on the post is "Epic refuses to pay out $1M bug bounty promised for discovering exploit"