Dude, I think the rugby guy was saying it sarcastically. You didn't need to offer the other side. What he meant was, he knows your weakness and wanted to exploit it (as a joke, cause he lost) but you could have stayed right footed and you wouldn't have risked hurting your knee all over again. You may have a different take on this point but I just hope you're fine. Clearly you won, bro. But I would be very careful not to give a challenger your weak side.