Everybody in the upper class definitely knows they are in the upper class. It's not a 'revelation' you get when you are an adult.
Likely quite a few people think they are in the upper class and really are not.
I'm going by classical definition here, not the 'new world' American version of upper class, which is usually just economic.
That's not the definition used by the person you're replying to, so I'm not sure what your point is.
There is only one classical definition of upper class, the other is the very generic 'economic' version.
The commenter is clearly not referring to 'economic' upper classes as he referred to 'behaviours' 'social standing' 'expectations' etc..
He indicated his family once had a noble title but sold it - this is definitely the classical version of 'upper class'.
You want a 'pop culture' reference for actual 'upper class' (though it's 100 years ago) -> Downton Abbey.
