It happens to me quite often when I am racing online.. nothing to do about it..

I think it happens when all the players at the server gets disconnected at the same time. The position that your at at the moment everyone gets disconnected is equal to what point you get. I was at 1st place and got +115 points :)

Decided to contact Nintendo about getting the points back and this is the response I got:

"Thank you for contacting Nintendo of America. I can completely understand your frustration, however there is no way for us to determine what caused the disconnection you experienced. Once you are matched to another player, the games are played peer-to-peer and we really have no control and no way to determine what caused the disconnection. Unfortunately, we are not able to grant or restore these points.

Sincerely,

Nintendo of America Inc."