most plausibly it's because it's a balloon carrying something, not just a balloon, and the bit that is worth shooting down is the bit that's not a balloon. the

most plausibly it's because it's a balloon carrying something, not just a balloon, and the bit that is worth shooting down is the bit that's not a balloon. they said the second object was freely drifting and not self-propelled or guided, so whether it's technically a balloon or just something that behaves like a balloon is kind of irrelevant to anybody who isn't working for whatever government department is tasked with analyzing it.