This is what can happen.

At best: demonstration vaguely plausible.

Reason: it is highly unlikely that the amount of concrete in the hopper shifting left and right via turning would supply a significant force upon the trailer at right angles (as demonstrated by the finger touching the rear of the trailer) it would more likely follow the inertia of the vehicle.

Braking efficiency would be a far greater concern.

there was a incedent years ago on the free way. hopper full, too fast and hit the brakes. well it flipped the truck and the cab was crushed flat. in a hurry to get to the next job. haha

Its more than plausible...it happened to me.  Hightailing it to a concrete plant to clean out.  Maybe 55 MPH on the 4 lane..it caught me when crossing a bridge with hardly any bump...all it took was just enough to get the whipsaw motion going.  If you have good trailer brakes, lock em down and the jerking stops real quick.  I found that 1/2 a hopper is much better than a full one!  If your trailer tongue isnt pushing DOWN on your truck's hitch, lose some weight on your tail.