For recreational purposes most likely? It's sad that this highly intelligent person has died, but drugs are a thing. And people do them, and sometimes it gets out of hand and those people die. There's nothing too unique about this.
I don't see why. Lots of people take drugs, they're very available in San Francisco, and that particular combination is famously risky. Sure, common sense would tell you that the risk isn't worth it, but people often take foolish risks in pursuit of a good time.
I do agree that the timing is very suspicious, and i'm sure this will be construed as some kind of conspiracy- but realistically, considering the kind of death; I think it's most reasonable to accept that this was a standard mixed drug overdose death.