I was invited to join a race, however the other player (the initiator) didn't turn up for the race for some time. Eventually I got bored and clicked OK on the 'do you want to stop waiting' button. A couple of minutes later, I get a notification that I came second in the race...
It seems to me that if one player quits the race before it's started, there is no race. While it possibly works out quite nicely for players who want that quest, it doesn't really make any sense for their to be a winner when there was no race...