HAL placed the 4-4. That was a relatively passive move, in that this is the first 4, so he is giving Adam too much freedom.
So, why did he do that? Well, hard to tell -- there are many possibilities. Maybe he didn't have anything interesting to play. After all, he should be repeating the 1's, but he doesn't have the 4-1 (you do!). Maybe he doesn't have any other 4? Maybe he has a lot of 4's and wants to leave the 4 alive? (remember, Mike played the first 4, but he played it hitting your 2. It is the second time that you played a 2, so maybe it's not that he played the 2-4 because it was such a good tile to play; maybe he played it because he's running out of options! (remember that he is trying not to hit his own 3). So it's not crazy the possibility that HAL might have a few 4's.
Anyway, we can not know for
sure, but we'll keep these possibilities in mind and see what happens...
Maybe soon enough we'll have more information that will help us choose
which of those possibilities is the one that is happening!