I've watched the reply at least a dozen times, and at super slow speed. While it's still not certain exactly what happened, this what I see.
1) I did not see Fisher step on the rail,. At least not before he started flailing.
2) I did not see contact with Mo. At least not before he started flailing.
3) I see Krop almost in lane 2.
4) I see Fisher almost on the rail.
5) I see Jakob start to pull away and Krop start to move back in.
6) Krop only had about 1/2 step on Fisher and Fisher was moving slightly faster.
7) Fisher starting running up on Krop and running out of room.
8) Fisher tries to chop his stride. He might be worried about hitting the rail. He's already going into a flail.
9) He might have slightly knocked the rail at this point. Impossible to tell. However, it was after the fact.
Basically, he ran out of room. Should Krop have moved as far over as he did. No. Was it egregious. No. There are running all out at the end of a 5k. It's packed. The blame is probably equally spread to Krop and Fisher. Fisher tactically put himself in a box. Krop moved over when he did not have sufficient room to do so (but this happens all the time).
It's wise to run on the rail during the race. It wise to run on the outside on the last lap, unless you are in the lead.