Ok, you have three components at work here. I can speak with authority on the 777, but from those I have talked to that should know, the 757/767 systems are similar.
First are the thrust reversers. For the reversers to deploy, the airplane must be on the ground, throttles must be at idle, and the respective engines must be running. Clue #1, the airplane didn't think it was on the ground OR the throttles weren't fully closed.
Second are the spoilers. When the spoilers are armed, they extend on the ground when the landing gear is fully on the ground, and both throttles are at idle. If they are NOT armed, they will extend when the throttles are put into reverse thrust. Clue #2, in addition to the above, the throttles may not have been at idle for some reason.
Third is the auto brake system. Auto brakes are applied when the wheels have spun up and both throttles are at idle. Clue #3, the throttles may not have been at idle. Or at least the plane didn't think the throttles were at idle.
The common denominator here appears to be the throttle position. IF the throttles were not fully closed, all three of those systems would not have operated properly. Given the design of the reverser levers, I can't see how it is possible that the throttles were NOT at idle. Stranger things have happened, I guess.
Having said all that, there is one other system that may have come in to play here. It is called an Air/Ground Sensing System. There are sensors on each main landing gear (Can you say "Squat Switches"?) that sense when the airplane is on the ground. Signals from those sensors configure various airplane systems to the appropriate air or ground status. If for some reason those sensors did not sense that the airplane was on the ground, I can see how the above three systems would have not operated properly.
From my post #67 in this thread:
How about if the thrust levers were not in the idle position after touchdown? Would the levers move to the deploy position but no further? That would not explain the apparent lack of ground spoiler deployment but it could explain why the reversers didn't deploy on the first attempt
Apparently, thrust levers not fully closed could explain a lot. So could a mechanical failure of the Air/Ground Sensing System. Time will tell...
An eyewitness reported it had snowed a lot the day before and the snow off the end of the runway was pretty deep. Lucky - Mother Nature's EMAS
Best,
GC