When four runners dropped Farah early in the race, I thought it would be nearly impossible for all of them to fade. However, it is quite possible they were going too fast.
When Farah passed Guye Adola, the latter clearly tried to hang on. But it did not last.
Stephen Kibet looked right until very late in the race. But when he started to fade, he faded badly.
An when Kogo and Farah made the last turn, Kogo seemed to know he would not be able to kick with Farah. There was no contest.
As much as Farah's last half marathon was fishy as hell (Mike Kigen stopped sprinting way before the line, just like he feared he could nip Farah on the line; and it was in the UK...), that one did not look fixed to me. A little weird (four runners fading), but nothing more.