That's exactly my story - we planned to visit the week before thanksgiving months ago based on rumored smaller crowds.
I was told by one hotel that there was a convention, but another said they hadn't heard of one. I tried anaheim visitors center a month ago and they didn't know, maybe they will by now. The number for the visitors center is 714-239-1340. They did say that conventions don't necessarily make DL busy, just the hotels.
Let's all cross our fingers!