Nice screen capture!
If the front wheel was turned perpendicular to the direction of travel then it would have been like slamming on the front brake, but that obviously didn't happen. I think that the old guy riding the bike was just a bit confused, and perhaps he made a random statement not knowing exactly what happened. It's not uncommon for people to not know exactly what happened when things go wrong. But the question remains, why did he grab his front brake so hard? He just came across a bridge with a nice concrete deck, then he crossed over a small amount of gravel before going onto smooth tarmac. At the point where things went wrong he was well away from the gravel and was on smooth pavement. Well, at least physically that's where he was but I don't know where he was in his mind. I think he just over reacted to something and grabbed the brake. After grabbing the brake his front wheel turned a bit and maybe he somehow thought that was the cause.
One of the reasons that I gave him the video clip on a flash drive was so he could see what happened, analyze it, and perhaps learn a lesson. I've found this kind of info quite valuable when analyzing my own motorcycle racing failures. Often what I thought happened was not what was shown in the video. It's just how the human mind works sometimes.