Why is Trump often viewed as non-establishment on this sub?

I’m really confused by all the support trump gets on here. The GOP is the major republican group. So why wouldn’t he be part of the establishment? Surely his antiestablishment stuff is an act for votes right? Like populism. If he wasn’t a millionaire and working under the GOP I might feel differently. But he’s never even lived a normal life. Please explain. I’m British so I’m hoping some Americans can explain.