Lasse Collin, the other xz maintainer, has acknowledged the backdoor

They haven't particularly made a comment on the situation so much as acknowledged it's happening. They seem to be going with the story that they had nothing to do with it and this is news to them. Hope to hear more from them soon so we can find out more about the situation, how and why this happened, etc.

(The sceptical tone isn't because of disbelief of Collin, it's because we don't know enough about the situation to be able to say Collin is or isn't telling the truth here.)