It's not a "loophole" if he someone is using the ticket between the origin & destination printed on the ticket, which he is.
If purchasing a ticket with a carefully chosen origin and/or destination other than the one you are using, to get a better price, that could be seen as using a loophole. There is no harm in doing this, it's still perfectly valid. It could be argued that loopholes generally occur because some Train Companies overcharge for certain journeys!
Whether it's a loophole or not is largely irrelevant, and certainly not worth falling out with people over, but in this case it isn't.
If purchasing a ticket with a carefully chosen origin and/or destination other than the one you are using, to get a better price, that could be seen as using a loophole. There is no harm in doing this, it's still perfectly valid. It could be argued that loopholes generally occur because some Train Companies overcharge for certain journeys!
Whether it's a loophole or not is largely irrelevant, and certainly not worth falling out with people over, but in this case it isn't.