The video involves a firmer approach to chi sao, although it can be said that wing chun is neither hard nor soft. It can be hard relative to a weaker person and soft relative to a stronger person. Importantly, the system is adaptive.
If you can ignore the striking, you will realize that the video also shows how the skin on the arms has been conditioned or trained to respond instinctively to attacks. You may notice that the teacher's (or sifu's) students appear unusually calm for the amount of punches that are being thrown their way. Later, you will see blind folded chi sao!