Flight attendant is black. Uppity economy passengers are white. Wonder of there was some racial animus in her comment. Even so, the economy passengers were wrong to try to stow their carryon in first class.
Where I have sympathy is that airlines often do not enforce the carryon size limit closely enough. Or, the airlines have crammed more seats into the economy section without increasing storage for carry on luggage.
I hate flying any US or European based airline. They are all horrible