- the balloon was required to file a flight plan or have an ADS-B transponder
- the balloon did not file a flight plan or have an ADS-B transponder
So either the balloon's operator didn't know about the requirements, which seems unlikely given its apparent sophistication, or the operator was deliberately hiding the presence of the balloon, in which case I think it's reasonable to call it a spy balloon.
Looking on from UK this all seems like a big joke. Slow moving, massive balloons, visible for hundreds of miles are sophisticated spying apparatus? But all the previous encounters over the years have just been unremarkable weather balloons?
- the balloon was required to file a flight plan or have an ADS-B transponder
- the balloon did not file a flight plan or have an ADS-B transponder
So either the balloon's operator didn't know about the requirements, which seems unlikely given its apparent sophistication, or the operator was deliberately hiding the presence of the balloon, in which case I think it's reasonable to call it a spy balloon.