I think the two events (your friends USB & your USB being on the same PC) was just a coincidence and nothing to do with your problem. The error you speak of happens regularly to people with USB pendrives, even when they've never used it on a different PC or even never taken it out of their house. It even happens to me about once every three months. So I think the Macintosh thing is just a "red herring".
All USB pendrives will eventually fail without warning and are therefore not suitable for storage of important files that you can't afford to lose (unless you have backup copies somewhere else). They are intended for "quick" data transfer jobs only.