Not enough info to know for sure what happened. I'm guessing smokeless powder was used. I have a collection of small cannons (.31 cal thru 1.0" cal.) and have fired several for effect only, no projectiles. Using real black powder and normal safety precautions it is a safe undertaking.
Many manufacturers ship replica cannons with the fuse hole undrilled. Many replicas do not have a wedge or screw for adjusting elevation. The absence of those is a sign the item was made for display or noise only, not to shoot a projectile.
This is very sad.