I think it is fairly clear that the captain was trying to abort the landing but using inappropriate actions. The report (in german) says there was no call for a go around instead the captain commanded flaps 20.
There were noises sounding like the speedbrake handle being retracted and Toga trigger clicking. The video also shows the nose raising. Both pilots kicked the rudder hard right which then disconnected the autopilot.
In rollout mode the autothrottle kept idle power and the aircraft rapidly decelerated. As they were now down there was no obvious benefit from taking off again. However I am not sure what stopped them steering back onto the runway.
As others have pointed out the appropriate actions which I am sure will feature in many people's next sim would have involved clicking everything off selecting go around thrust manually and rotating appropriately.