Well, as someone who has had to maintain multiple such airgapped networks you are obviously in the know that this could be done, because you've done it before.

The point here is: they didn't even try.

They could have easily temporarily cut off the segment that this was running on, or restricted and monitored its egress to the point that a hacking attempt on an outside party would have been detected.

The point here is (again): they didn't even try.

So yes, they obviously should have either done that or they should have not run their experiment given that they are claiming that the models are intelligent enough warrant such concern. In fact they post one article after another about how much smaller and less capable models are intelligent enough to warrant such concern and in fact warrant regulating this domain to the point that only they are able to own and operate this stuff.

Let's make a biology analogy: if you can't safely operate with harmful substances that doesn't give you a license to do so in an unsafe way. Then you just don't do it.