That is remarkable...
At takeoff, ruffly, the trebuchet would have had about 5500g of radial acceleration going on... and for a 0.4kg mass (what does it weigh? 100gms), the force of the release is around... 22KN... and a velocity of around 330m/sec. That it then popped a hole in the tub is not a surprise. What is a surprise is that it was tenacious enough to hang in there until the takeoff, that takes some amazing schtick.
The imbalance on a prop is surprisingly well damped by Mother Earth when the plane is on the ground, once airborne, all bets are off and the vibration can be spectacular...
Back in about 84, a certain "Brand X" P3C ripped up 2 star pickets, and tore the cuff off a blade which was not noticeable on the ground, but got the total attention of the crew as the gear came off the ground. Was a short flight.