That’s what I had noticed. IIRC, we concluded that it was most likely peculiar to SitePoint Premium handling the login process and not a core Discourse issue.
That is, if a member had been suspended in the forum, they should still be able to access their Premium account, and when they logged in to Premium the event was sent to the forum anyway.
My guess is that the login modal (screen in SitePoints case) was updating the last seen at the beginning of the log in process instead of on its success. But I haven’t looked at the code involved yet so I don’t really know.