While o don’t this it’s a threat in training, it should be stated that air gaps have been bridged before. Example, stuxnet

But that was through transfer of data. If you don't transfer data, at best you can do what that one researcher keeps pumping out with like ramping fans up and down. But really you'd need to try. Unless the model has some controllable USB switch, physical network separation should do it. I'll also add that modern network security practice is that data flows one direction only. But ideally you're never bringing untrusted data in. Especially never out

I don't think it's necessary to state that something isn't perfect when pointing out that it's still strictly better than something else.