The problem with references is that not everybody gets the reference, and without that (and possibly even with) this is a death threat. And with today's highly polarized and volatile political situation, you need to be really careful with that.
I've come to expect this sort of behaviour from random internet trolls, but a CEO really should know better. I think this counts as a disqualifying lapse of judgement.
Either way knowing how to communicate responsibly is part of a CEO's job, that's one of the reasons they get paid so much.
Dealing with people in management positions disabuses you of this notion.