Nothing Sipr is going to have a wi-fi. At least, not at the tactical level. God knows what goes on with secure cellphones and stuff. However a Sipr computer is still a computer and if you hook in the wrong cable then you've breached the network. Any bad actor knowing where the ship is and with sufficient information is going to try and drop malware to the router. That malware would load to any computer attached and if it happens to find itself on a secure computer it then attempts to phone home or cause havoc.

Which is why hooking a green cable into a red computer usually means you unhook it, power it down, cart it off to IT, and then hope the punishment isn't too bad. (Ranges from push ups to half pay for an honest mistake.)