Technically, the other fob shouldn't be affected if it works the way I think it does. There's usually a maximum number of keys synced to the vehicle.

This attack basically forces the key fob the flipper zero is substituting itself for to fall out of sync because the flipper zero doesn't transmit the rollover response from the vehicle back to the key fob. So the F0 sends the rolling code it intercepted from the key fob to the vehicle. Vehicle is like, yep, that's matches, and then it does it's rollover and sends out the rollover response. The response doesn't get back to the key because of range etc and then the key remains a step behind the vehicle in the rollover sequence from then on out.

Technically I think ~~they~~ the key could potentially be resynced to the car. (My understanding is that a key of the correct type could be synced to any car that it can be programmed for so long as the key isn't physically damaged, and the security module isn't compromised with malicious code that would prevent it).

Yeah I would assume there's a maximum number of fobs you can register to an individual car and it just keeps the state for all of them individually