Unless you've ever lived in a big city and commuted regularly by train, you wouldn't be aware of how silent riders are in rush hour, especially morning rush hour when the trains and stations are most crowded. A single person making small talk on their phone annoys everyone.
The mistake this guy made was running his jammer continuously. If you have jammer and want to target one person on a cell phone, you only have to momentarily switch on the jammer when the other end of the call is talking. When the rider is chatting, you leave the jammer off, when the other end is talking, you turn it on. Within 30 seconds, the caller will give up. Using this approach, your jammer is only on for a few seconds at a time.