At the incredible speeds Starship was moving (>13,000 mph) by the time it was over the Caribbean, debris from a Starship is expected to burn up by the time it reaches the surface. But you said "depending on the size", so let's imagine it's a different spacecraft carrying something that won't entirely burn up, like the Mir space station from several years back.
In that scenario, debris from 100km will survive to pass through 10km. The point is: if the mass becomes debris >143km high traveling at >13,000 mph over the Caribbean - it doesn't pass through 10km anywhere near the Caribbean. Even though the friction causing tempered metal to glow white hot is slowing it, the trajectory is ballistic so by the time it slows enough to get that low (10km) it's hundreds or thousands of miles East from where the explosion happened (and where that airplane was).
It's weird because given these orbital velocities and altitudes, our intuitions about up and down aren't very useful. Starship exploded in orbit over the Caribbean, so planes in the Caribbean were safe from falling debris. If it was Mir instead of Starship, planes hundreds or thousands miles to the East of the Caribbean would be at elevated risk. My high school astronomy teacher once said something like "Rockets don't go up to reach orbit. They go sideways. And they keep going sideways faster and faster until they're going so fast, up and down don't matter anymore." While that's hardly a scientific summary, it does give a sense of the dynamics. You'll recall that Mir was intentionally de-orbited so it would land in a desolate part of the Indian Ocean. So, did they blow it up right over the Indian Ocean? Nope. To crash it in the Indian Ocean, given the altitude and speed, they "blew it up" on the other side of Earth, like maybe over Chicago (I actually don't recall where the de-orbit began, but had to be very far away).