Obviously this sort of behavior is not nice to have out the gate, but keep in mind you've barely gotten to know him since these are your first days aton the job.
- Being the Chief Technologist, he may be "rough" like this in internals and e-mails to be more direct. It may not be something personal.
- As observed, it is a hard to match the pattern (specially with 2 days); While it is no excuse to chew out your co-workers, perhaps they are having a bad week on top of it.
- As stated, the toxicity is "implied", and the CTO has apologized to you (was it in public?).
And as you've said, everyone else in the team is friendly; the workplace you're in already seems to have a culture in place which isn't predatory.
For now, I'd recommend not taking it personally and possibly escalating as it may be a misunderstanding at this point in time.
Get to know your co-workers, and once you know what to actually expect from these different people with whom you'll be spending a lot of time with, you can start drawing conclusions and raising complaints.