The more I look at it. What I am seeing is when he lifts his leg, then looks to 1st, then back home when he comes to the plate. I don't really think it's a balk, but it is a little different than when he goes home withuot looking to 1st while in the delivery. Maybe the ump just saw something different and called it a balk.
On that last video, look at pitches at 0:48, 1:08, 3:27 & 5:08. Each one of these I saw the look to first in the middle of his delivery. On the last two, it is a little more evident that when he looks that way, he turns his front shoulder a little more towards first. Just an observation that the delivery looks different than all the other pitches and maybe that ump took that as a balk. Let me know what you think.