Motorists don't drag along dogs on unreasonably long and dangerous dog leads.

Sharing is a two-way process: if a path is supposed to be a "shared" one, then pedestrians as well as cyclist need to make an effort to share it. Walking on one side of a path with your dog on the other, and a dog lead between the two of you, is not sharing.
My post may have been exaggerated a bit for the sake of humour (well in my head). But the point is still true.
Battering a guy and his dog because his dog was in the way. Is no different than a van driver battering a cyclist because he was in the middle of his lane instead of "sharing" it.
When threads like this come up, they tend to drift towards "dogs should be under control". But the argument isn't too different to "cyclists should be in the cycle path". It borders on victim blaming.
While the papers will report this as "cyclist" doing this. It is no more than a bully on a bike. Would he have done the same thing if the walker was a well built mid 20s guy?
I
believe that amongst younger cyclists, there is a growing trend of entitlement. The attitude may have come out of a necessity to not get squashed by cars. But it is often misdirected.
Try walking on a road against on coming traffic (as you should do) when footpaths are extremely busy. And see what reaction you get from cyclists trying to use that area. I have personally seen a trend towards a certain age and gender group that seem to have an "issue" with it.
Personally when out on a bike, if it's a shared footpath, or down the canal tow path. In my head, this is primarily a pedestrianised area. As such, I give them right of way in my head. On the road you're traffic. Pedestrianised area, you're traffic still. No different in my mind to driving a car through a pedestrianised area, they should be given space.