He's not on Facebook or Friends Reunited or My Life because he doesn't see the point. As he says, what sort of meaningful conversation can you have, with a stranger you once knew, if your only reference point is something that happened decades ago in school? (Cue Sandy Denny or Kate Rusby singing 'Who knows where the time goes'.)
In writing fiction, emotional shorthand can be used to establish a connection between two characters. Whether it's someone reacting to familiar music, dialogue reminiscing about a specific event or some small passing clue, the reader feels that there's a history to be discovered. It's like being in on a secret and that sense of intimacy not only gives the characters depth, it also draws the reader in.
The English poet John Donne wrote that 'no man is an island'* and we exist in a sea of interaction. Social media, one could argue, is swamping us with waves of quantity even though we're thirsty for quality. In writing, everything matters or else why put it in at all? We - and our characters - are always responding to both internal and external stimulus. Mr A acts a certain way with Ms B because she reminds him of Mrs C or because he and Ms B both fell in love with the same woman and he lost out. A personal story, well told, makes for compelling listening and reading. Even if the person happens to be someone else's creation!
And the photo? Well, as Charles will immediately recognise, it's Emma, one of the best friends I ever had. Yes, she shrieked when excited, like a kettle about to explode; and yes she tended to pong a bit after going into the sea (and sometimes even when she didn't); but she was quite simply a brilliant dog. Heart of gold and brains of sawdust, and brilliant.
* Except perhaps the Isle of Man.