I'm sure it was a bug, as someone on the previous page said it was not intended to give credit. But in undoutably did. It popped up in big yellow letters, I watched my monthly advance, and other than mining some resources in Southsun, I haven't set foot in PvE this year. I assume they fixed it immediately, but if people are in LA, might as well pop in and see if you get credit.
Edit: Oops, nm. I was going to see if it would credit me on a different character, but the Wintersday stuff is gone after the update a few minutes ago.