They would have received braking action reports from either the tower or the two company jets that landed in the previous 13 minutes. They knew what was going on and what they were getting in to.
They felt comfortable enough to do it and not go missed, go around or reject the landing. If something did go wrong on the landing rollout and they were slow to the point that a reject landing was impossible...they made the right decision in staying on the runway.
It's just too sad a young boy is going to miss christmas.