I cannot answer all those questions about dog walking business owners because I am not one nor do I have insider knowledge about that business.
>> Do they care about being better dog walkers, saving time or money?
I'll go out on a limb here and say "YES", if you own a dog walking business, you care about saving time or money (or making more money).
That being said, I can answer all those questions about other niches (photographers, hackers, restaurant owners, churches, etc.) because I either am one or know that market. So, that gives me a pretty good starting point for identifying needs, doing deeper research, and then creating a product that meets those needs and that niche market is willing to pay for.
That is, in my opinion, what both posts were saying (in different ways).
Do dog walkers hang out together online in a place you can identify? If not, how will you learn about them in a way that's natural & not manipulated by their feeling of social obligation or desire to be nice to you and positive about your ideas?
Do they hang out together? Do they talk to each other? Do they spread information on products they love, do they help each other and recommend things? Do they care about being better dog walkers, saving time or money?
If not, they share demographics in common, but they're not a market in the sense that I teach in my class.
For a niche to be a bonafide market, for the purposes of creating & selling a product, there needs to be a solid segment which thinks and behaves in the same (pro-commerce) ways.