Update: talked to some peeps in the stadium who were at the start. Said they saw him step over the line. Probably because he was off-balance as they shot the gun. Basically ran in the wrong lane for a couple steps.
Thanks for posting the video of the races. Holt looks fine on the start line, clearly behind. The video doesn't show him running the first 50m or so. I do notice the official raises a yellow flag on the first turn - the first official not the one around the 100m point.
so apparently he stepped on the inside lane line...they could've let it go but they didnt, according the the USATF rules handbook, there was no material advantage gained so they could've let it go but they wont!