Well no one knows God’s ways, hence us always saying God’s mysterious ways. But I’d say God puts his grace in all kinds of places. If a person is not Christian or Catholic it doesnt mean they can’t act with God’s grace, just that they dont know it. Any good act anywhere in the world is God’s grace, always. Anything bad is mankind. Simple really.
I am pretty sure that the passage in Luke (12:48 especially the last part ) means that God entrusts more to some people, ie Christians are baptised so in other words He has given them/us His spirit so he trusted us with more so he is going to expect more from us than non Christians, well by that I mean people who never seriously get the chance to learn about Christianity, not people who learn but reject it. We are called to holiness and some to different levels such as priests, religious, lay etc. So I think God means we will all be judged differently according to how much he has entrusted us with during our earthly life. So people who are given less will be judged less and so on. Jesus is completely just more so than we can imagine so this makes sense to me to explain what you have said. Everyone can choose to be good or bad in their lives whether they know why or not or who they attribute it too, they can choose. This is God given. How much He chooses to reveal of His nature to them is really His business, but I dont believe He will ever judge them unfairly.