(If this is dominion, this is my experience)
The "poll pads" talk back to the county server where the voter information files are housed.
They connect via a wifi hotspot known as a 'mifi' device. MIFI allows for multiple connections kind of like a home router.
Each poll pad has a configuration on it that establishes a connection to the Cellular network (tunnel) which connects to the county server.
Jovan's dude hacked it in Fulton county GA last year sitting outside a polling location.
Dominion argues the poll pad isn't connected to the internet. However, that's a generalization. It requires the internet to establish the link and then setup some type of private network (vpn/tunnel) to talk to the county server.
The nuance of 'not on the internet' is exactly mincing words. It cannot function without the initially establishing a connection to the public internet via the MIFI device.