Well it looked to me like the spectator tried to push or shove him.
Now you can jump through all kinds of mental gymnastics to claim he wasn't intentionally pushing him off the bike, merely overcome with such support for MvdP he felt he needed some assistance to move forward after his poor start.
Or however you want to square the circle, fact is your arm/hand doesnt unintentionally move outwards like that and you were attempting some weird come on fist pump encouragement within the fence boundaries of the course and simply were unprepared for how close & fast pro riders are.
The guy also didnt look remotely shocked, embarrassed he'd made contact with the MvdP afterwards. Though didnt clock if he disappeared after that lap.
I can understand why MvdP downplays it, but its still like the vaper guy just another add to the list examples of bad crowd behaviour towards him at these races imo.
Nobody got hands on with the riders in the women's race, why is it always in the mens and always MvdP who gets it.