Watching that vid, it seems like a normal landing in terms of descent rate, flare, touchdown and initial rollout. What stands out is the subsequent lack of spoiler deployment and reverse, followed by an excursion onto the grass and the nosewheel raising briefly.
The speedbrakes should auto-deploy if a) they are armed, thrust levers at idle and on the ground or b) if reverse is selected on the ground. They are re-stowed if the thrust levers are moved forward towards takeoff thrust.
The nosewheel lifting appears to coincide with the left gear going onto the grass, judging by the dirt being kicked up. I wouldn't have thought that could cause any significant pitch up, more likely the opposite, so that leaves the possibility of an attempted go-around from after touchdown, aborted soon afterwards. Possibly the engines spooling up at different rates leading to a directional problem? TAC *should* have dealt with most of that as they were most definitely >70kts. A bit of a poser, this one. I wouldn't want to point any fingers at the crew until I knew what was working/failed in this particular instance.
As far as the aircraft shooting off trying to follow a false localiser, from the 777 manual:
The autopilot flight director system (AFDS) can detect significant ILS signal interference due to service vehicles or aircraft. If localizer or glideslope signal interference is detected, the autopilot disregards the ILS signal and remains engaged in an attitude stabilizing mode based on inertial data. Most ILS signal interferences last only a short period of time, so there is no annunciation other than erratic movement of the ILS raw data during the time the interference is present. If the condition persists, the annunciations described above for Autopilot and Flight Director Mode Degradation are provided.
I would presume the filtering carries on during the landing roll.
Replaying the clip (which I think is almost undoubtedly genuine), I have to say how lucky they were not to have had a major accident. I've never seen anything that size in a 14-wheel drift from the grass, across the runway and back on the grass again. If it had dug in a little more or pulled in a different direction, it could have gone through rows of parked aircraft or even into the terminal. Once something with that sort of rotational inertia starts spinning, all bets are off...