And - I've seen service dogs the size of Corgis all the way to a really tall dog that looked kinda like a really tall black and white shaggy dog.
Which leads me to the next point - I WAS surprised they'd show footage of Joshua petting a service dog. While the owner may have allowed him to pet the dog, I hope that he did NOT just do it without permission. The reason for asking is because the dog is "on duty" and you're potentially distracting him from helping his owner. There IS a chance that the dog is actually a therapy service dog, which would allow Joshua to more freely interact with the dog.
So that said, please - if you do not know this already - if you see a service dog with an owner, do NOT go and pet the dog, and if possible walk on the opposite side to where you are between the person and the dog if you must pass the person in a store or other area. This helps the dog not be distracted (especially if training - and yes they wear vests to show this), and helps the person. Yes some will allow you to pet the dog if asked, but not all do, let alone some cannot.