You're assuming he had the level of knowledge of this event that you do. I'd put my house on the fact that he did not at all. I understand his anger. Lying about the situation helps nobody and only makes things worse.
They pepper sprayed him, were in a lengthy standoff with him after he'd assaulted two people, in the video you see him swing the knife at a Garda's head just before he gets shot. For Jesus sake like this is cut and dry. I understand the lad's anger as that of any bereaved family member. But this is flat out lies that are being tossed about.