Interesting that this was caught on film like that.
I have not heard anything from within BA
as to why this happened, however:
have recently been emphasising during simulator training the need to keep an open mind about going around even just after touchdown if there is a perceived problem with conditions or the amount of runway still available. They have also been stressing that the non handling pilot (non landing) should remain alert and 'in the loop' all the way through short finals and the landing - sounds obvious, but it is very easy to 'switch off' when you think it is an easy day and you have a very competent pilot next to you performing the landing(especially when you are tired after a long sector)!
So, during the recent past, we have been practising go-arounds from very low or after touchdown (baulked landings) in the simulator.
I would say that the video does not show a hard touchdown nor a 'bounce', so I would like to think that there was another reason, such as a deep touchdown, a technical problem or maybe the crew saw a runway infringement further down the field and elected to 'discontinue' the landing.
In any event, the aircraft appeared well controlled as the gear was retracted shortly after becoming airborne again, so I think that shows that the crew were well on top of it and not struggling to keep up with the aeroplane. They presumably landed off the next approach, so no harm done and the safest course taken.