Any time you have a wheel off it is generally recommended that after 100 miles or so you check the wheel nuts to make sure they haven't come undone. This is safe practice.
In saying that every single time I have checked the wheel nuts after a wheel was removed and then put back on the wheel nuts haven't come undone in my experience. Doesn't mean it can't happen though.
It could be though that the garage put your alloys back on whilst the car was in the air, nipped them up and then forgot to fully tighten/torque them up once the vehicle was lowered back down to the ground. Seen that happen before.