All good advice in this thread so far.
Looking at your first post in another thread, it did seem as the bike needed a bit of TLC. If the rear tire was actually reversed, it's certainly possible the shop wasn't terribly concerned about aligning it either. If alignment was way off, it could cause the bike to feel more natural turning one way or the other. It would have to be way off, and this is unlikely compared to all of the other likely reasons listed above. But if you continue to gain skill and comfort, and the bike continues to feel somewhat strange, it might be worth re-aligning the rear wheel. If you do get that tire flipped around, make sure it's done well at that point.