Being ‘staff’ should not preclude involvement in a discussion and maybe all staff should have a disclaimer statement in their footer bit stating that any views expressed are personal and do not represent (etc etc).
HOWEVER, I would concede the point made somewhere in this discussion that the forum itself ‘Technical and account support’ does imply a degree of authority to ‘staff’ on subjects posted therein. I would agree that, the comments made, could by the nature/title of the forum, be construed as advice and that imho are probably not the best way to deal with such emails.
in this case maybe the best solution would have been to move the post to a different forum?