If I gave a reason, it would be pure speculation because no one would no why. I think even if he made a mistake it was still a good-will gesture to partake in a tradition that is not of his own faith. I would be honored if say, an atheist came to my Christmas party with unwrapped presents. It would be a gaffe, and not part of the Christian tradition, but I would still think it was kind and nice of them to observe my holiday when they really didn't need to. So overall, whether it was lack of attention, or he got caught up in the moment, or ignorance, I think it was nice of him to partake in the lighting of the candles.

Thanks, good answer.