There’s no great mystery to this, but then it is DOG we are talking about so maybe he meant ‘inexplicably’ after all.Can you "explain" why they are linked then?
Both organizations spring from the same root. This is not new. Throughout the troubles many people, but not all, held dual membership but even then, there were IRA members who wouldn’t vote SF in a month of Sundays.
Since the ceasefire and the disbandment of the IRA, bar allegedly, the Army Council, then IRA members and supporters were encouraged to use solely peaceful means to further their political aims. That many would choose to do so through the party that most closely represented their views can’t be a huge surprise to anyone paying attention.