How fast do you need to go...?
...to break a puppies leg? Not very I would guess.
I must admit that most of the time I use the Taff Trail is as a runner, and it's generally cyclists who annoy me the most with their behaviour, acting as if they have right of way and everyone else should get out of the way for them.
That said, I do also have to regularly hurdle/sidestep unleashed dogs, so can understand how the collision in the article would have happened.
Seems like another example of different groups of users not taking account of other groups and adjusting their behaviour accordingly.