I read that comment as saying it doesn't require touching fiat. Bitcoin is a currency, so doing any sort of store-and-forward of it makes you a money transmitter.

> For traditional Bitcoin mixers as in this case, someone receives money from users and then transmits money to many users. This is money transmission and requires registration with FinCEN and sometimes requires registration with states (though some states have exemptions for completely crypto to crypto transmission that doesn't touch USD or other fiat).

Some states having exceptions for pure crypto transmission implies that most states don't.