General consensus is you have it in one - anti sand bagging measures.
Get to Legend and it's 500 counting RRs as a Legend to TL, and 60 average threshold. Couple of TLs blow that rule apart but basically that's it.
V careful playing Ls / TLs in MP when you are below below L though as beating one can be one V fast way to become a Legend.
EDIT: See this thread. I think Donsprintr nailed it as much as anyone can re the the point he had.