Covering/ sealing the small area between the cylinder and the handle can cause an explosion. You can lose a thumb doing that (saw it on Mythbusters). Not sure it can cause the type of explosion shown here, though.
If there is something lodged in the barrel, it may cause that type of catastrophic failure.
SnakeDoc
I’ve seen a revolver barrel with THREE squibs splitting the barrel.
I also witnessed a double squib at the range. The second round sounded like a cap pistol going off.
And yes, the second incident was with re-loads.
Never saw a cylinder failure like that, though.
Only if the obstruction was close to the chamber, if it was down the barrel, near the end, it would not cause the chamber to blow up but rather the barrel would split. Two chambers blowing like that is damn near impossible, IMO, one chamber, yes. Two?no.
Sealing the gap between the barrel and the cylinder doesn’t have any effect on the pressure in the cylinder chamber.