Well, that bollockses the "stuck rudder pedal" nonsense then doesn't it?
Nose wheel steering should easily overcome any rudder input on the landing roll.
If the rudder was (indeed) jammed, keeping straight on the landing rollout would be a non-event.
Jez.
Given that the change in direction comes only a few seconds after touchdown (so @ Vref -20/30 kts?) I seriously doubt any pilot worth their salt would have their hand on the tiller. If he/she did they need re-training.
The time between veering left and straightening up (albeit on the grass) suggests use of the tiller after they left the runway or the cause of the diversion being removed.