Remember that it's an ultralight. With full fuel maybe it can carry two hundred kilos of people. If you have no people to fly it, you have to fill it full of stuff to make it fly.
Have a look at the system in this Cessna. It does not look light. Assuming you still have 100kg to play with, that would be in the ballpark of people saying it looked like a 50kg plastics explosion. Hard to know how the environment around the explosion affects our view of it. For instance if the plane went through a wall, concrete roofs may have suppressed the fireball. You can bet the Ukrainians (who know what they loaded the plane up with) are very carefully analysing every shred of info they can get. Even in that footage they can count all the smashed windows (sadly I believe the drone didn't hit the factory but the dormitories next to it) and get an estimate of the force. That's just the footage we see right now. They'll be trawling through eyewitness accounts, all footage available etc. even looking at the mushroom cloud is going to tell them something.
https://www.airandspaceforces.com/cessna-turned-drone-foreshadows-future-unmanned-opportunities/