I think he sent Jess home as he really liked her parents and he was never going to choose her, so now was the week to send her home as he didn't want to hurt her sweet parents.
Or as someone said, he realised her family weren't as loaded as the others! Either way, Sam should have rejected his rose. He's clearly not picking her! She's the 4th wheel for sure.
If I were Jess I would have told him to get stuffed, why should she have had to have justified herself that late in the piece. Grow some balls and just choose your 3 favourites. What a tool!