Seriously? Historically trains have been subjects of terrorism, when they were the most popular transport, and if they managed to blow up those trains in Madrid back in 2004 in the train station(supposedly secure) imagine how easily they can ambush or simply derail them while they're in transit.
Yeah man, he's right. The fact that trains aren't subject to as tight of security as planes makes it so you are actually more likely to get fucked up on a train. While 911 was some bullshit, it was kind of a singular event. Terror happens much more frequently on other, more mundane types of transport, like buses. Or, sans vehicle, in the case of mosque explosions or the recent Europe vehicular homicide attacks (perpetrated with a vehicle, but the victims were pedestrians).