I do not know the location. Could the truck be using the wrong lane to go round. A bigger combination vehicle might have to do so for either direction of exit. For that your local knowledge allows for even greater indignation.
Please do not advocate for the Australian rule: "The vehicle with its wheels on the roundabout first has the Right of Way." In the depicted situation a boy racer could easily get a new paint job from any in road.
Play nicely children.