Edit. for some reason i cant post a picture (SS from youtube).
I've paused it, and you can clearly see the "yellow" ball there, he's hitting a little high, I'd say 10cm higher than rules. but the motion/movement is not illegal or weird, it's just he didnt give enough space to serve so he couldnt tuck his elbow enough to hit it lower. you can hit downwards, with slice, at belly high, as a serve.
This one? if it was an "ace" I'd say fault, if not i'd keep playing.