“The Englishman had probably been radicalized in prison, possibly as a survival tactic.”
I think that one needs to be predisposed in order to become radicalised.
The guy you met on the train was most likely born into disadvantaged background (Midlands?) and had no decent job in his life.
After his term(s) in prison his chances of finding a decent job are even lower so he feels that somebody has stolen something from him, something that he was “owed” by the virtue of being born in UK.
As always it is much easier to turn and blame Jews/Blacks/Asians/… After all he is unlikely to blame himself for his own inadequacies.