This kind of comment is designed specifically to garner attention. I assume the attention being generated is why TPM leadership is standing behind the comments.
I highly doubt that any of them actually think the government is trying to exterminate Maori. If it was actually case, I would expect a case being raised at the ICJ and massive international attention. Even with the wars going on, a western democracy that is part of various international alliances going from very liberal to hard fascist in less that a year, would cause massive international attention.