Being as close to a Legend as you were I don't know why anyone would accuse you of cheating. I routinely beat tour legends and lose to tour masters so it all evens out in my opinion. Beating a legend will speed up your movement to Legend, which I assume you already have done, so if you were sandbagging you aren't doing it very well.
My view of the WGT sandbagger is someone who get to tour pro or master and quit playing ranked rounds so they won't go upward. They keep playing and get all the good clubs and balls, but don't want to move up, so they play only in rounds that are for credits and play enough ranked rounds with bad scores to keep the number down.