No, not really.
Aside from "How many dogs can you walk at one time?" the question perpetuated by Hollywood and apparently Manhattan (answer: 3, I live in neither of those places), the second most popular supposition is "You must be in really good shape."
I mean ... Ok I have 8 to 10 visits a day. Some of them, especially in the summer and around the holidays, are cats. No, I don't walk the cats. I scoop their litter and feed them. (That's the third most frequent question. Cue the Scarecrow's musical number).
Other days, yes, it is not uncommon for me to walk 10 miles or more. It depends on which dogs I have, every day is different. If the dog is elderly, stubborn, or a puppy, we're prolly not getting very far. No matter who I'm walking, we need to stop for potty, to smell stuff, and say hello to people and pooches. It's not cardio or anything.
Dog walkers, while we may have lower blood pressure and better tans, still need to exercise. Some of us even struggle with our weight. We like to come home and binge on chips, salsa, and reality television just like you people. For me, personally, I follow a plant based diet and try to jog approximately 8k and hit the yoga mat once a week each. The jogging increases in the spring and fall. If I'm crazy busy at work, then I don't have to beat myself up about not exercising. And, awesomely, I can sometimes turn my last walk of the day into a jog. Why the last walk? Because sweaty dreads itch and I need to get home and shower STAT.
Now, let's all do some sun salutations.