That is interesting. Though I'm not sure that even if one of those came loose it would allow the door to move. There are supposed to be four bolts installed and if just one of them is installed I'm not sure how the door could move up.

https://www.youtube.com/watch?v=maLBGFYl9_o at around the 7:26 mark has a great explanation of how the door is secured and it seems like as long as there is at least one of the four bolts installed the door can't move. Now as you pointed out those loose nuts could effectively mean that bolt could become useless. And the NTSB didn't mention those other nuts, which I think they would have.