Juggernaut crash

David 8 became Pinocchio with the Covenant crew when explaining what happened to the juggernaut, Dr. Shaw, and an "accidental" disbursement of a black cloud of death on the local population. 

It's a mystery, maybe Dr Shaw crashed it to stop David who might have wanted to go to earth and do the same thing. Or maybe the other engineer ship fired on it and it crashed.

I think and hope that this, amongst other questions will be answered in the next movie (feels like I've said this before …).

We will see indeed...

I'm glad everything wasn't fully explained in this movie. You always need a bit of mystery. But I wouldn't be surprised if we see more of the Engineer's scorpion ship, and what it can do. It wouldn't surprise me if that ship had tipped the juggernaut into the side of the nearby mountain when they figured out they were under attack.