Bletchleyite
Veteran Member
I've left the train at Milton Keynes Central actually on my Crewe to London journey with West Midlands Trains before because I ran out of water and was thirsty. Of course there is absolutely no provision at all onboard on WMT. This of course is not permitted even now by the ticket type (Super Off Peak Return) but fortunately WMT chose not to enforce their onerous restrictions.
While there is no official definition any more, convention for many years is that Break of Journey is constituted by "leaving Railway property when this is not necessary for the ticketed journey" and not simply by changing trains unnecessarily. So what you did is fine.