M.F.
I think your hunch is correct about that your son is upset about selling your house. He is too little to express to you his feelings (or all of his feelings) about this so it is coming out in his potty behavior. We have to put up our house for sale shortly and my 6 year old is having major problems with it, although at this point he is able to express it to me. Some of the things that I am doing to help my son are not getting rid of any of his toys. As much as this kills me because I don't want to move all of them as he has outgrown many of them, it is just too hard for him to give them up at this point. Another thing we are going to do is to make a picture book of our house so that he always will have a memory of it. My son is painting pictures of our house, but for your son you could take pictures and put them in a little book. I am not sure how far you are moving, but if your son's entire world is going to change then you could include other things in your book such as a picture of his favorite playground, etc. I think with the potty behvavior, just keep reminding him to go. It probably will pass in a week or two when combined with helping him with the house issue.
One more note, we also moved when my son was 2 1/2. I didn't realize it at the time, but it was really hard on my son, much more then I thought it would be. For example, prior to the move he would go to the doctor without any problems. After we moved, he literally sreamed the entire time we were at the (new) doctor. So, even though they are little it is hard for them to go througha change. it took my son a long time to get adjusted to all of the new things. In retrospect, I should have helped him more with all of the changes rather than just expecting him to roll with it.