Damnit boy little to close for me!!!!!

Seems like it was still within arming distance and the warhead didn't detonate?

I agree. Judging by all the dirt thrown up, it appears to have hit terrain while still within pre-armed range. Might have been a berm that was being used as camouflage.

what happened here? I couldn't see what it hit.

N00b gunner. Stugna seems to dodge down a bit before the main rocket starts. Thats why they usually are situated on a small mound and aimed initially upward. On flat ground this might happen.

Honestly not sure how you can figure out what went wrong from this angle with limited amount of frames the rocket is actually visible in the video. It could be either faulty propellant, snapped guide wire or pretty much anything. Those rockets have poor manoeuvrability and flying so fast that a slight movement of the tube would not cause crash to the ground. From the footage I can see the rocket crashed further to the left rather than at front of the tube indicating it could be caused by stabilisation fin that did not deploy correctly or was damaged.

Just an educated guess based on how we've previously seen them situated...