See for yourself. An expat from California measured the radiation level inside the train to Narita, and found it was extremely high right where he was sitting.
No, it was not his suitcase. It seems it was that particular seat where he was sitting.
Yes, his personal survey meter could be broken, as he repeatedly wonders in the video, and people just ignore the gaijin telling them the radiation level inside the train is the Fukushima level, while a woman sitting next to him praises his Japanese as native level. Surreal.
This line, Sobu-Yokosuka Line, belongs to JR East, which covers the entire Tohoku, Kanto and about half of Chubu.