Perhaps you were lucky, and they were in a sheltered position; fleece would certainly have helped keep them warmer.
If I had done that with my seedlings, here, with the recent minus temperatures/hard frosts - I'm sure none would have survived. When I moved trays of tomato seedling indoors for the night, I missed a tray - by the morning they were blue, from which they rarely recover.
So you have to have some idea of the plant's requirements and your local conditions - and not make silly mistakes