It didn’t need to be a marathon runner. Just faster than what it was hunting. And with a battery of teeth like that, and a set of toenails like that, hands really are an unnecessary option.
As for using Hyenas as an example, Horner demonstrates exactly what kind of fool he is. They are VERY effective predators.
Just like the old joke about runners fleeing from a bear.
The first runner says to the second. “What are you doing? You can’t possibly outrun a bear!”
The second replies: “I don’t need to outrun the bear, I just need to outrun you.”