I don't think that's true. It's possible to simultaneously be pro-Bitcoin and also believe in Keynes's approach for the pre-Bitcoin world

There will be multiple fiat currencies in use, alongside Bitcoin, for multiple decades to come and it's not clear how best to manage that. It'll be a new world, and I don't think we can blindly accept or dismiss any existing approach. Austrian economics might not be the perfect approach, even though some bitcoiners love it