“The cup contained traces of peanut oil, so it seems clear Simon died from that drink. What we’re trying to figure out now is how peanut oil could have gotten into his cup.”
I will theorize That Simon Put peanut oil in the cup himself. He probably didn't have a lot of friends Because of The 'about that' app and telling people's secrets, So he was probably depressed And the thought of everybody hating him and not trusting him likely got to him.
The other option is that everybody in that room Was in on it And covering for each other.