Wouldn't a scan of the e ticket provide details of the customer either via the Trainline account or the bankcard used to purchase the ticket? If so, perhaps the ticket examiner prefers this method rather than ask the passenger details which may turn out to be false.
I'd agree that it wouldn't be particularly good practice but then again do all TOC staff follow set procedures? Without knowing exactly the actions of the Revenue Protection officer and the lack of detail in the OP, it may be that the passenger was 'offered a second chance'.
I would certainly echo the advice given that the passenger should in future ensure they hold a valid ticket for every journey so as not to find themselves pulled up again by revenue protection.