He is very right. They were popular, and even more so now. It's easy to classify bands into genres because that's how companies sell records. I wouldn't go so far as to call them a boy band...at least, not by the definiton we have today.
What does him being an American have to do with anything? We can like them just as much as you can, and we're entitled to our opinions just as much as you are. Stop being a stereotypical prick.