Saying I have no idea what living somewhere could be like: 'None' completely rules out any sort of empathy.
A strange take IMO.
Especially given that the UK and US are culturally very close. Far right populism is a thing we deal with now, isn't it?
You can have empathy and still acknowledge that somebody living it will know more than you do. Maybe it was too far for them to say 'None' but passions are running high.
I can't speak for the person you were responding to but that is how I saw the interaction. You saying 'I know', the other person saying 'You really don't the half of it' and then you saying back 'Yes, I do, I know all of it'.
I agree with you, we come from a similar culture but I have compared things about the UK with my American wife and more often, with examples, I have had my thought process altered to believe that it really is not the same level.