Such a 'defence' would indeed require 'evidence'. The appropriate 'evidence' for 'having paid his fare' would be a ticket, presented on request. That evidence is strikingly absent, therefore the 'defence' is unsubstantiated.
Your missing out the fact that where no ticket is presented he can give his name and address as an alternative. See here.This is the law RORA 1889 sec 5.
So it is not an offence. I would have thought you of all people would have known he could give his name and address.
So no offence.