Other fans have done far worse, I think it's a bit mean-spirited of Cav to have picked on one hapless teenager and belittled him in front of his peers; the poor lad will never forget that.
I take your point, but I think it's starting to become a persistent problem so this might have been the result of a building irritation.
At this year's TdF I was on the last corner/village, 5km before the drag race to the finish. There was a minor off involving two riders. Immediately a spectator shoved a selfie stick in the riders' faces until one of the riders gave him a shove, more to get him away as he tried to untangle his bike rather than aggression. As the road was tight, the support cars had stacked up behind so one of the (neutral?) mechanics had to sprint with two spare wheels to get the riders going again. Monsieur Selfie managed to get in the way of all this as well until another spectator dragged him out of the way.
What really gripped my merde at the time was that it was obvious M. Selfie was more concerned with getting himself in the frame with the riders than actually following the race in any meaningful way. The race just provided a backdrop for his own #myawesomelife. A deux chapeaux of the highest order.