If they are running Linux why would you be worried about MS Windows licensing?
Because I've heard scenarios where people were demanded to install
the auditing software on every machine regardless of it's use or risk
confiscation and it leads me to believe computers with OEM licenses
are a factor. However, admittedly I’m having trouble finding where I read this.
That's crazy and should not be a concern. Nobody is going to force you to install software on your computers. Even if they ask you to do it, you can refuse for reasons of security. Your PCs, your network. Especially on machines that aren't even running their OS.
Maybe the one Windows computer is
volume licensed. Maybe it's not a license that is triggering an
audit, but an anonymous tip. I'm looking at a worse case scenario
where they somehow weasel their way to recognizing all PCs,
regardless of use or lack there of, need to be in compliance.
A single VL is not a reason for an audit. Especially a physical visit.
Something seems very wrong here.