Isn't it potentially a replay attack the poster is describing?

In a simple form it seems like this: The attack is you have a briefcase that contains specific RF transceiving components in it. You turn the brief case on in a hidden place, leave it, it records data, you come back to it later, and then press a button(s) that replays those RF signals.

Perhaps, there's some very weak cars that don't even need a replay, but are vulnerable to a master key, or bruteforce, or something else.