As a retired police officer (34 years) I post’m as I see’m.
Ok, that explains it. The section of the video you identified shows the law enforcement officer on the scene grabbing and pushing a citizen who, as far as can be ascertained from the video, is not prior to or at that time violating the law in any way. Given your perspective you probably can't recognize an assault perpetrated by a police officer, even when you watch it on video. I doubt the potential jurors or the public would be so blinded by their personal perspective.
That's why video recording is so important. Without it at trial the police officer would, like you, say he was attacked. And based on the charge of second degree assault, he has apparently already made a sworn statement that the attack on him was sufficient to cause personal injury to him, which seems, in the light of the video, to be untrue.
The video of course shows that the officer actually touched the citizen first, without any legitimate reason, and it appears, before he even identified himself as a police officer. And then the officer pushed the citizen, causing the citizen to lose his balance.
I would suggest that it is highly unlikely that the officer will testify under oath that he was attacked or injured by the citizen given the presence of the video recording.