He was riding with an activist (also claiming to be a journalist or film maker?) and that was all a setup. I think JC learned a valuable lesson there, as he was caught out in a number of ways. Momentum not being as clever as they thought.
I was once down in Carmarthen to see an old friend, and got one of the non direct trains to Cardiff on the way back, changing at Swansea from a TFW service to a GWR 10 coach IEP and like any good rail user, I walked down the entire length of the platform to the front of the train in the knowledge it would be a lot quieter there.
After a little while a couple of guys come up, on the phone to someone and say that there are plenty of seats in the front coach and we have a table next to another table. About a minute later, Jeremy Corbyn comes in with another one of his handlers and takes a sit down at the table, having attended a function in Swansea. They clearly did not book in advance.
A couple of people with the trolley and checking tickets came past and just smiled at him and treated him like any other customer. But then there was a couple of announcements in relation to the train manager contact the driver and other crew type messages and a short while later, the train manager came up to speak to Jeremy and introduce herself and they talked about things.
I was only 3 rows back, quite well hidden and lets just say some of the conversation between Corbyn and his handlers/advisers was interesting to say the least to hear how the Political PR machine works and how calculated it is. I assume they felt as they were talking very quietly and I had headphones on I wasn't listening, but it just showed me that all politicians generally have many moves highly calculated, in terms of time, tone and message, with PR in mind, even if the travel itself wasn't flagged ahead.