He (and I) were not talking about Chassidim; we were talking about Chareidim. Chassidim are Chareidim; Chareidim are not Chassidim. It’s not the Chassidish aspect that makes them Chareidi; it’s the fact that they fit the definition of Chareidi in other ways (ways that have nothing to do with being Chassidish).
I actually would agree with you that Chassidus is a new movement although that doesn’t necesssarily make it a problem. That is why there was so much (necessary) opposition to it when it started. On the other hand, even though Chassidus was originally a new movement, one has to keep in mind that Chassidus of today is very different than it used to be, and non-Chassidim of today are different as well. The Chassidim would probably say (and perhaps correctly so, at least in America, and at least to some extent) that today, they are actually the ones holding on to the Mesorah of yesteryear and the rest of the oilam has become modernized.