The Diocese of Spokane has a blanket dispensation from attending mass since COVID broke out. Also, there are Catholic churches in Pullman (both off and on campus), Moscow (both off and on campus), Colfax, Uniontown, Colton, Palouse, etc.
There are a lot within driving distance. Indeed, my wife's cousin drives nearly 80 miles--one way--every Sunday to attend mass (though the Diocese of Boise has a dispensation for those more than 50 miles from a parish).
I'm not Catholic, so I don't know, but would they really even be able to tell you who attends, who doesn't and how often? The Catholic masses I've been to, there's a LOT of people. I suppose they could tell you if they've literally never seen a person at mass.
I just have kind of a hard time believing WSU reached out to confirm the attendance of over 400 people who claimed a religious exemption.