Some two years back one of my friend got his I-485 approved in three months from TSC, that poor guy was thinking of getting married before the approval but for everyones surprize he got it in three months. When I was talking with my lawyer about it, what he said is for training purposes they randomly pick some cases and work on them. Your friend was I think one of the lucky ones who got picked up, good for him. Ask him to buy lottary ticket or something he might even win it.