Unless this lion was crippled I find it very difficult to envision landing a solid blow with a flat head shovel on a moving cat to kill it. They have an 18 foot vertical jump with reflexes like lightning.
There’s more to the story....
That guy was extremely lucky, or something.
I have spent a lot of time with improvised weapons and while a normal yard shovel can be used very effectively against in-close fighting with a face to face human, trying to fight a mountain lion with one seems very awkward and mostly just something barely adequate to hold it off if lucky.
The cat was on the dog, an easy hit with a shovel.