Ummmm - hate to break this to you, but a SIM card in a device other than a phone is only used for data-communications over a cellular network - especially connections to the internet. If the SIM cards are removed AFTER the polling hours have concluded, then that indicates they were installed DURING polling hours.
In other words, they had all that was necessary to be connected to the internet, and therefore accessible to others via the internet.
(Respectfully) I think this was just a misuse of the term. A SIM card is specifically a card for cellular communications. I think what is being used here is a standard flash-based storage card of some kind.