Fisher did not step on the rail and whoever says so really can't see at all. Watch that video at 3:00 and put it in 1/4 speed.
This is, however, Fisher's fault for being in a stupid position for the second time in 2 races. He threw away two medals by marrying the inside rail.
What happens here is that he tries to pass inside of Krop because he didn't put himself in position to go wide, while the rest of the field (starting with Mo) is starting to move on the outside the way anyone with a brain would be positioned. Grant tries to go inside Krop, but Krop is ahead of him and drifts back in to protect his position, legally wrecking Grant's momentum. Grant tries to hold the position, makes a brushing contact of his right leg with Krops left leg, which pushes Grant's outside (right) foot to plant just inside the rail. Now Grant's inside (left leg is coming though in such a way as he would step on the rail or off the track so he counterrotates with his upper body to keep his feet in the track. At this point Mo is moving outside and around which leaves Grant nowhere to go so Grant has to rotate back to keep his feet on the track, which wipes out his forward momentum as the rest of the field begins passing him. He's now going out the back door and hangs on for 6th.
If he was on the other side of Krop's legs on that turn, he gets bronze at worst and quite possibly gets past Krop for the silver.
It was a great championships for Grant; we learned he is capable of double medaling which would have been amazing, but he needs to watch those tapes and get on the outside of lane 1 before 200m to go so anyone behind him has to go to lane 2 to get around. Going inside looked like it was going to be brilliant because he was behind Jakob so he could expect not to have someone slow down in front of him, but he was not fast enough to hold Krop outside. He should have took the outside instead, ran aside Krop (which he was doing) and then used the energy to try to slingshot past Krop forcing anyone behind to go to lane 2-3 to pass. By going inside, Krop expertly closed him off which ended his race right there. Mu did the same to Keeley in the 800m - dangled the inside line to her, then closed off the path once Keeley committed to it.
Time for Grant to watch tape. Maybe they need to do interval workouts where they repeatedly set up these kind of packs so he can practice positioning because he's totally capable of medalling in either or both events now.