I'd imagine the Clio driver somehow ended up trapped infront of the lorry at an intersection, the lorry driver did not realize this when the lights switched to green and just went, probably thinking the subtle "bump" when he picked up the Clio was just a rough gearchange.
If you can't imagine him being unable to see the car, go sit in your own car and check how much of your bonnet you can see from your normal driving position, now imagine the same without a nose infront and much higher. The space the nose would occupy if the lorry had had one was occupied by the Clio, I reckon you could put 3 Clios there (1 adjacent to the one in the video and one ontop) and you'd still be unable to see them from inside the lorry cab.