My guess to reasoning is that they called a startup founder a sociopath who would kill people to make a profit.
That said, that was a completely defensible and evidence-based thing to say in context (the founder threw a fit about regulators who wanted to know what the chances are that people would die), so unless HN is cracking down on the casual use of "sociopath" by people who aren't making professional medical diagnoses (which, to be fair, I do find objectionable, but not to the point of hellbanning), it seems like it was for no sensible reason.
It isn't always possible to figure out from the public data why an account is banned.
When a banned account's comment gets vouched for and rescued, we look at the account history and unban it if we see that we banned it unnecessarily (we try not to do that but it happens) or if the commenter has reformed. Alternatively, there may be a good reason for the account to stay banned, but if it posts good comments, HN users will vouch for and unkill those. This system has proven to work well, even better than we hoped when we introduced it.
That said, that was a completely defensible and evidence-based thing to say in context (the founder threw a fit about regulators who wanted to know what the chances are that people would die), so unless HN is cracking down on the casual use of "sociopath" by people who aren't making professional medical diagnoses (which, to be fair, I do find objectionable, but not to the point of hellbanning), it seems like it was for no sensible reason.