Families cross paths 70 years apart

I have been researching my family history. My father's family were predominantly from East Lancashire but in the 1881 census they were shown to be living in Durham where my GGrandFather was working in the mines. The family moved back to Lancashire and in the early thirties my father moved to Bristol to find work and subsequently moved to surrey before the war again for work. This meant that I was brought up in Guildford. I have been in touch via Friends ReU with a few of my old junior and senior school friends and have found out that one of them acts as a Family History researcher for people and had a colleague who specialises in military matters. Because one of my grandfather’s brothers was a mystery, being unable to find any DoD for him though we had been told he didn’t return from the war (WWI we thought) I asked my friend to try to ID a uniformed photo we had of this missing GUncle, in passing I sent him a copy of the 1881 census entry. He then emailed back to say that his GGGrandparents were living next door to mine on the same census. He had no connection to Lancashire and his family had only crossed with mine, there in Durham and later in Surrey.