May the Lord of Christians forgive me if this is a sin, the pastor is probably accepting Bitcoin because he understands that it can't be traceable by anyone, since it's church offering.
A pastor taking Bitcoin as offering is quite questionable, why would he even consider to do this aside from the fact that those money being paid are laundered or cannot be traced, don't let religion make you assume that the questions you ask about this are not valid or they are a sin, we are supposed to think logically when it comes to situations like this because it's actually not right.
There's definitely more going on here that a lot of people are yet to know about or perhaps he has his reasons for taking these funds in Bitcoin.