Clearly, the dog is the inspiration for this canine idiom.
We can also say, his bark is worse than his bite.
Many dogs are scary because of their loud, fierce bark but often, if you are not frightened by that, you might find the dog is not as bad as he seems - so it is with people.
The phrase is often used to describe a manager or dominant personality who may shout a little but be quite soft at heart and OK once you get to know them.
"Our new boss was a bit intimidating at first but then I realised his bite wasn't as bad as his bark."
All the same, a barking dog can be a nuisance so here's some training on how to quieten a dog that won't stop barking! But as usual, it's actually the owners, not the dogs, that need training.
This guy (American) speaks pretty fast so you'll need to focus.