C.J.
Hi C. -
Because your son did not quite make it to the three week mark, when habits are truly formed, he may have just had a great practice stretch at being potty trained. I say this only because my daughter at one was "potty trained" for about two weeks, and we all thought that she was some kind of prodigy - WRONG! Turns out that she was just practicing. She's two now and nearly completely potty trained, but we're not pushing her. She's doing everything on her own, and it's great. My son was three years old when he was potty trained for the day, and 3.5 when he stopped wetting his bed. Most boys take a bit longer to get potty trained, so at 29 months, I wouldn't worry too much about your son's relapse. He'll come around again especially if he goes to preschool and sees the other boys going to the potty alone.
Blessings to you and yours!