Yes, but it doesn’t look like a storm drain to me. There is no grating in it, as you’d expect to see in a storm drain, which could cause a cyclist to crash. No, it looks like a solid, metal utility access door of some kind to me. A little rough to roll over on a bike, granted, but not a reason to choose instead to ram a cop.
I think you are right about the lack of storm drain grating, but every additional time I look at the video in full screen mode, I see the cop move quicker to intercept the biker in order that he can deck the biker. If the cop fell to his knees, I’d have to suggest that it was the momentum of his exploding into the biker that caused the fall. JMO.