Well as the reporter said - OMG!
Good thing the finish line structure wasn't more substantial. Local hay carters wouldn't know if they're over maximum legal height or not.
If that finish line was as high as the legal height for a hay truck (which from a quick google is 4.6m), then that truck was over the legal limit by a good metre. So personally I suspect it was something else, either (a) the finish wasn't high enough or (b) the truck wasn't meant to be there.
Actually now I think about it, a bigger concern is how close the truck was behind the cyclists! By my watching of the video, it's only about 3-4 seconds behind. What if the cyclists had had a spill? Weren't there road closures?