It's a shame about friends crashing. But if you go through a curve with no issues and the next guy lowsides, it wasn't you that did it. It was different tires, different riding style, a different line through the curve, and maybe a few dozen other possible issues or combination of issues...over which you had zero control.
One of the guys I've ridden with periodically not only crashed when he rode with me and no one else, he did it three times in a row over the period of a couple of years. Yeah, I was a little hesitant to invite him along for a while, but he's done better the last couple of times out.