Furthermore, Will's tweet here about WWOTF implied to me that he didn't know Elon personally: https://twitter.com/willmacaskill/status/1554378994765574144

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Which part implied that to you?

Presumably the part where Will says "So, er, it seems that Elon Musk just tweeted about What We Owe The Future. Crazy times!" I agree that this is not something you'd say about someone you knew to the extent that Will knew Elon to the extent shown by the Signal messages, unless you were trying to obscure this fact.  

Elon was keynote speaker at EA Global 2015, so would have known Will since then.

In Bayesian terms the update should be in the direction of EAs being less trustworthy than the average person, if you agree that the average CEO of a firm like FTX wouldn't have done what SBF did.

believing in EA probably explained a lot less variance than SBF's idiosyncratic character traits (e.g., plausibly dark triad traits, especially narcissism and Machiavellianism which entail immense lust for power and fame, disregard of common-sense morality such as not lying, etc.)

In my experience a disproportionate numbers of EAs have dark triad traits, which is not surprising given that a disproportionate number of EAs are mainly in touch with their heads.