Come on, 99% of the carry ons that people take on board probably wouldn't fit in the sizer, but they fit in the overhead. It's not like he was trying to take a clearly oversized checked bag through. It is still a carry on. For F pax and group 1, there is no reason for them to be making issues over the size. GA was on a power trip.
And those that decide to take bags that are outside the permitted dimenstions should be prepared to accept that they may be refused boarding with that bag and accept with good grace when the agent does check.
That it was a Tumi or that the person had 100k loyalty points is completely irrelevant EP status does not confer any rights to take larger hand luggage
A GA enforcing the published rules is correctly doung their jo b - not at all reasonable to call it a power trip.
If the bag did fit in the sizer then the OP would have reason to be upset, but that doesn't read to be the case