Yeah, not telling anyone is actually good advice, mostly for your safety. I don't think you should've returned the money, but I don't know the whole situation and I suppose you had reasons. The most important that the lesson was learned.
It is better to return the money to the man than to have him tell others all his life that you cheated him and that he lost money because of you. Back then it was a sum of only a few hundred $, but today that BTC would be worth a real small fortune. There is an old saying that people learn best from their mistakes, especially if they have something to do with money.