I don't think roleblocking has anything to do with it. If Cheshire's ability was blocked, why would it only block fox's info and not all of ours? Since we all touched that same ball on the same day before Alvy held onto it.
GM shenanigans is always a possibility. But you could say that about nearly every thing in every mafia game.
Now, a possibility of roleblocking is possible if Fox's own role states "Anyone who targets you with an ability gets roleblocked". But I still wouldn't believe it - technically Cheshire never visited Foxrally. Plus if Cheshire got blocked, then how would he still get info on the rest of us? :P
With the info we have, assuming Foxrally is a "secret" role that can't be investigated easily (coughepochcough) is the most likely option. Mind you, it may not be right - but with what we know at the moment, I think it makes the most sense?