https://ncaa-football.myfootballnow.com/gamecenter/view/133#24359

Was this a case of the CB tripping over his own feet or some other physic that we cannot see?

Or is this the CB randomly slows down bug?

There is a 'trip' type penalty probability that increases as M2M skill decreases, especially when the WR makes a cut. (It's never non-zero, so even a 100-rated M2M player may have it happen, but it will happen more frequently as M2M skill decreases)