It used to happen to my dad all of the time.
Once on camping holiday in Cornwall we went out for the day to a nearby town. As we walked up a shopping street dad as greeted by a work colleague. Neither knew the other was even on holiday that week never mind where they'd be going. Further up the street we met another of his colleagues, who similarly didn't know where we were holidaying and was surprised to hear of the presence of the guy we'd met not 100yds back. Turning the corner we bumped into his secretary with her husband who was yet again amazed to hear of two other colleagues, although she did know where we'd be, as in somewhere in Cornwall, they were staying in Devon, but had gone out for the day over into Cornwall. As we all lived some 400 odd miles away, my mother's comment about a 'works outing' went into family history.
Similar meetings, with a single colleague, seemed to occur nearly every holiday ranging from in Scarborough, relatively close to home, to Norfolk, Scotland and Wales.
Dad had a 'big personality' and was well liked by most of his colleagues.