I don't suppose it matters if they were following a rowboat or not, sounds like bad form to me. Any person or persons who are taking up whole width of path need to be aware that people will be coming the same way, faster than them and from behind.
I almost wiped out a kid on one of those little scootery things today on the Roseburn path. Convoy of parents and dogs strung out across width of path, I passed slowly on their left in the very narrow space they grudgingly created. Kid shot out from behind one of the adults from where he had been hiding into the space I was coming through. I managed to swallow my curse and wobble into the grass.
I dislike the "walking" of dogs from back of a bike. Personally I don't think even a very well trained dog is under full control if it's off the leash - owner is dependent on dog's willingness to obey commands. An interesting smell or some curiosity / aggression / amorousness on the part of the dog is enough to overcome that. They're even less under control if the owner is on a bike trying to watch what their dog is doing rather than where their bike is going. And those riding with the dog on a leash are a downright liability - the dog is in control of the owner.