I don't think he is. I did a skim of the US DOT 2011 Level Boarding ruling which grants exception to platforms adjacent to freight railroad traffic, but not to platforms serving mixed railroads. Here is the September, 2011 Federal Register entry. My interpretation is that if the Miami Central Station were to start construction now, at a minimum there would have to be mini-highs for the Amtrak trains. Since the platforms are much longer than needed for Tri-Rail commuter trains, a mini-high or short high level segment could be placed at one end of the platform with a ramp. The level boarding requirement will complicate building new stations in the east that are outside the NEC and direct connecting corridors.Trust me when I say you are simply mistaken.
But this is a moot issue with respect to the MCS.