The author clearly has no clue whatsoever how it would actually work if it did. I can see feasable ways they could detect analogue/digital broadcast (not any earlier than perhaps mid 00s though), or with iplayer over WLAN or WAN (assuming the RF protocol in question hasn't specifically engineered ways to not be able to identify playbacked data patterns, which most data-protocols actually do or they are considered to be flawed encryption).

What is unlikely, is that they would actually have this all over the place actually doing anything. There's no way that could even be remotely cost effective at all. The license fee would hardly cover such operations alone. So yeah obviously their only aim is scare tactics, which means they don't even need to bother actually having any detector vans. They probably do mess around with a few just so that they are technically not lying (they don't even have to work well for indisputable evidence, just in theory), incase it bites them in the ass in the future.