It seems a little strange to me that your friends would say not to take a picture of a cute cat - I'd consider that entirely normal - and it makes me wonder: is it possible there was something ELSE about that photo they were talking about? If you got very close to someone's window, close enough to see well inside their home, or took a picture from that close, maybe that's what they were advising against? If not, I'd say your friends are wrong about what reasonable boundaries are or are even fucking with you.