for example - you don't need a passport to travel from the US mainland to Hawaii. It doesn't matter that the aircraft cross international waters, it matters what country you were in last.
The US DHS agents in the US make a choice not to fuss over the airplanes or even cruise ships sailing from US ports to Hawaii and back. They could, but they don't. They probably validate the ship or plane's location via transponder, but it wouldn't even surprise me if they don't do that for regular commercial transport.
This kind of local and specific policy is great and it is enacted in lots of places within US jurisdiction.
For this purpose "country" has to be interpret as stepping on any land outside of the US.
"Land" is legally (and generally) defined as pertaining to planet earth. In this case the crew did not step on any land outside of the US. The moon does not have land.
Interesting. Where have you read this? Intuitively, it seems very weird for a lawmaker to specify the planet the law would apply to.