It seems likely that the mods talk to each other and critique one another's decisions. It's quite reasonable to say "we" to mean "the moderators of HN as a collective group" if banning your account was a group decision. The fact you're getting a comment from an individual doesn't mean it was necessarily just that person's decision to ban you. It's pretty uncharitable to assume moderators don't take their 'job' quite seriously.
Also even if the moderator made that particular decision alone, he will not have to stand up for it as an individual if it gets challenged. Any sensible organization will back him up as long as he acted in good faith and did not break some basic rules. He is, at all times (except when not acting as a moderator), representing a larger entity.
(They might of course still have an internal disagreement over an issue, and maybe take internal action for bad decisions, and might overthrow that decision if warranted, but not by blaming it on one individual.)
