In this situation, does the strong lateral wind pose a danger to the motorcyclist and other road users in the vicinity?

In the video you are coming out from under a flyover on a road outside town, behind a motorcyclist; on the right there is sign A-19 "crosswind", leaves and small bits are flying in the air, and the motorcyclist is drifting towards the centre of the road. A strong crosswind creates a hazard for the motorcyclist and other road users nearby. The answer is: yes.

Sign A-19 warns of a place where strong crosswind gusts may occur - such as the exit from under a flyover, where the shelter suddenly ends. The Road Traffic Act requires you to drive at a speed which ensures control over the vehicle, taking into account the weather conditions, and to keep a safe distance when overtaking - at least 1 m from a motorcycle. A strong crosswind affects a motorcycle much more than a car: a single gust can push it a metre to the side, and correcting its path makes it ride unevenly. So the motorcyclist may suddenly end up in the middle of the roadway or right next to your car. That is why you increase your distance behind them, you do not overtake in gusts, and if you do, then with as much lateral clearance as possible; you also hold the steering wheel more firmly yourself.

Legal basis: Art. 19 para. 1 and Art. 24 para. 2 of the Road Traffic Act (Prawo o ruchu drogowym); § 10 para. 1 of the Regulation on road signs and signals