Artemy is probably as far removed from Catholic as they come. He's described his own religion as an Earth cult, and not only that, but he was meant to succeed as a religious leader of sorts of said cult. A pagan spirituality by all means that absolutely predates Catholicism. Even if he had been interested, the town he grew up in didn't observe Christianity, it's Cathedral having nothing to do with any sort of religion at all, instead something built by the Kains in their own madness.

And it wasn't as if Artemy was bound to convert, not in the slightest, but he had grown curious. He wanted to know how other religions conducted himself. He wasn't a very worldly sort of man, and all of these different holiday traditions that just were never part of his life? He found himself curious about all of it.

So there he sat. In the back of the church, simply observing. He asks no questions, participates very little, and refuses communion, as it does not feel appropriate, in his opinion, to partake of another god's flesh- of course he does not know that he wouldn't have been proper for him to have anyway, but, you know. He refuses on principle nonetheless.

Artemy walks out, feeling like he's learned something, and being glad he participated in an act of interfaith, but also being reaffirmed in his own beliefs.