Agreed... a bunch of highly trained fighter pilots mistaking unidentified craft that move in highly erratic manners at high speeds with balloons seem pretty far fetched.
I don't know, if moderate wind turbulence can cause a multi-ton airliner to bounce the altimeter by 10s of feet, than I can imagine it also moving a ten pound balloon enough to be characterized as performing erratic flight maneuvers
Especially a ballon filled with reflective spinning cube, aka Radar reflector.
This theory makes a lot of sense and would imply perhaps an adversary has been spoofing advanced radar systems.
edit: Also reports of underwater disturbances would be consistent with the concept of these being launched by submarines and ... maybe retrieved by them.
While I agree, it's impossible for us to tell who might be responsible, I wouldn't dismiss foreign subs as easily detected. AIP diesel-electrics are the quietest things out there, and Sweden has one of the best.