Collusion between players?

Question for the board:

I have never had this situation happen to me and was wanting some input on whether this is collusion or not and what I should do if anything.

Late stages of a $100 sng, 4 players remain and blinds are 500/1000. I am utg and push allin with the shortest stack, next to act folds then SB raises to 2000, BB raises all in and types in that he has KK, SB responds that he has JJ. BB tells him he better fold, he does. Cards turn face up and BB has KK. Is there a more blatant type of collusion among players? Should I turn them in to the site?

As a sidenote, I sucked out on the BB and won the pot and then ended up taking both of them out in successive hands and winning the tourney.

Anyone had a similar situation happen to them?