Neither. If she chooses to be that way, that's her life. Just because she's female doesn't mean she was forced into this. (and really, it's because it's degrading that people are into it. Read: masochism) The point of the article isn't either of those things anyways.
"We don't let freaks and dogs like you on."
Personally, I find that offensive. I may not be into the human pet thing, but I have my own fair share of kinks, and no one should be called out in public like that by someone like a bus driver just because they're turned on by different things than the rest of the population. (although I do believe that stuff should stay in the bedroom, but that doesn't change the point) I understand it as a health concern (but really, I don't think the couple would mind if she held onto her own leash for the ride. I highly doubt that everywhere they go he always holds it. He probably puts it down when they're sitting) but the comment is un nessecary. Yes, it's weird, but its their life and their choice. Be professional and keep your comments to yourself.