Initially I thought at 16s there's a brake light, although it's not easily visible against the yellow of the bike, however (having watched it carefully several times) I'm now not so certain.
You can see the nose of the bike dip just about that time, and I think it may be the change in light on the rear of the bike.
As far as I can see, the car does slow down (judging by the red and white boards on the central reservation) when the bike passes and then accelerates, however I have the feeling that some of the initial impressions may have been caused by the headline and text which says the biker gives the driver a "filthy look" and then "brake checked" the car.
I'm wondering whether actually, the biker has caught up with the car and is going "ok, let's race", but then screws up his gear change, causing the bike to decelerate as the car accelerates with the results as seen.
Whatever the case, he was bloody stupid!