That is a slight misunderstanding of what air-gapped means.
Imagine a world, only a few years after the stone age, when there was no such thing as WiFi or any other ubiquitous wireless technology (such as Bluetooth or cellular). So the only network connections were wired ones. So …
A computer or network is air-gapped from an undesirable network (usually but not always the internet) if and only if there is a “gap of air” between it and the undesirable network i.e. not plugged in to the undesirable network, and therefore safe from the undesirable network.
Now add wireless networking to the picture. The term air-gapped is now technically incorrect because it is misleading, and hence out of date (but still of course in widespread use). It is no longer sufficient to have a “gap or air”, an air-gap. You now also need to police all wireless networking - and that is more difficult.
The truly paranoid and very well resourced (coughTLAcough) might take a belt-and-braces approach and use extensive RF shielding on the facility and maintaining physical security of the facility and physically searching people on the way in to and out of the facility and have a spectrum analyzer sniffing for breaches and use 802.1X and …
@reC on the other hand will just ensure that, at its simplest, neither the wired networking nor the wireless networking on the Librem Mini is ever used. A more complex arrangement allows an entire private network but the private network is physically isolated from and radio isolated from any device that is ever connected to the internet - so in that situation you would use networking on the Librem Mini (probably wired only) but you would have to manage and police connections to the private network.
In my opinion a truly air-gapped arrangement for the average home user would be unacceptably inconvenient - but it does depend on your threat model. If you are coming up against nation states (whether your own or another) this would not be unreasonable.