Nothing that they will want to share with us.
I would expect they have been recording the transmissions from that equipment since it was launched. They might even have broken the encryption of the messages. And they have telescopes good enough to read the labels on the exterior surfaces.
They might even have spies who told them about the program.
Whatever they have, this is not a "Court of Law" and the notion of "Innocent Until Proven Guilty" does not apply.
The balloons are from China. They are conducting a variety of surveillance missions, one of which is provocation testing. The game has been going on for decades and everybody plays.