Ah yes, "likely air-gapped", what a high-confidence statement. Any competently designed air-gap must be precisely auditable and demonstrably, positively air-gapped.
The only world where "likely" is a reasonable word is in reference to possible physical taps or a precise enumeration of physical access points that went unaudited, but have reliably followed safe access control/configuration procedures. Anything else is plain incompetence.
KCNSC is a large organization that will have hundreds of distinct networks at different risk and control levels. Every variation of "public internet" to "single-site air-gapped network" probably exists there, including many levels in between like multi-site secure networks and networks with limited internet connectivity. Many networks air airgapped, this sometimes means that they consist of a small number of assets in a single room, and it sometimes means that they have connectivity to airgapped enclaves of AWS and hundreds of other military, government, and contractor sites. All of these controls will have been determined by a combination of risk scoring, compliance policies, legal requirements, office politics, and happenstance. Multiple contracting authorities will periodically audit many of these networks against various standards, which may or may not allow connectivity to specific other networks depending on risk levels. Connectivity between networks is sometimes controlled by NSA accredited cross-domain solutions and multi-level security systems that enforce complex policy, in other cases it's controlled by an administrative assistant with a DVD burner. There will be case-by-case risk analysis decisions made for specific systems, ultimately signed off by a government official who may or may not have read them. Inevitably some of these will appear reasonable and cautious in retrospect and others will not.
The root fault with this article, and the resulting discussion, is the extent to which it generalizes over one of the larger organizations in a very complex part of the defense industrial complex. Many parts of KCNSC's operations are absolutely not exposed by this incident. Other parts absolutely are. Determining which fall into which category, and to what extent that is acceptable, keeps quite a few people employed.
They have multiple networks. One of them is definitely airgapped (red for RD). The medium security one is protected by annoyingly strict network ACLs (yellow for ITAR). Then there's a low security one for stuff like sharepoint (green).
The standard you linked literally talks about: "High Impact BES Cyber Systems with External Routable Connectivity" and "Remote Access Management" for "High Impact BES Cyber Systems". That explicitly indicates non-airgapped critical systems. Furthermore, the proscribed auditing specifically spells out "network diagrams or architecture documents" as good evidence. Obviously, that is a high level document, but I see nothing to indicate robustness against state-level actors which are a expected threat.
Speaking from past experience with the DoE (I'm happy I don't need to deal with security like this anymore), there were constant and randomized checks to make sure fiber cables (they were all fiber to make it harder to tamper with and to avoid accidental RF) were fully visible (e.g. not hidden under a desk or something) and not tampered with. Also, lots of locks and doors, both electrical and mechanical. The guy at the front desk with a big gun probably helped too.
The only world where "likely" is a reasonable word is in reference to possible physical taps or a precise enumeration of physical access points that went unaudited, but have reliably followed safe access control/configuration procedures. Anything else is plain incompetence.