It is even more complex than that: I do not see PieFed.social in Hexbear's blocked instances list (click Blocked tab to see it on that page), so if it is true that HB has blocked PS, then it must be on the "hidden list" that Lemmy instances sometimes use to block communities or instances that they don't like, but which for whatever reason they prefer for that fact to not be as publicly visible (it also allows finer-grain resolution to block only certain specific communities such as Chapotraphouse without having to block an entire instance).
I am not sure if PS has an exact equivalent of such a hidden list, but even more than that, PS blocking HB is reputably done baked right into the codebase, at least turned on by default unless an instance admin specifically removes it.
But anyway no, if HB has blocked PS, then HB users will never see any content from PS anywhere, under any condition. Visiting some other instance, either as a guest with no account or as a registered user with an alt account, would allow this, but at that point the user would not be a "Hexbear user", in that specific mode of interaction.
