I can't even remember when I first heard this expression in CS. It feels like it was already an idiom when I was in university in the early 90s. It also felt like it was tapping into a general cultural background I already had growing up in California. It did not require any explanation.

Without being able to cite a specific TV ad or other urban legend sort of baseline, it clearly communicated that you hold yourself and your products to a higher standard. As a dog-food producer, you don't just meet the minimum requirements for legal sales, but you make it well enough to be fit for human consumption too.

It's in the same category as someone demonstrating that they could safely drink or breathe byproducts of some other industrial process. And, ironically, there was also a widely understood corollary that we could expect PR types to do something like this while secretly fearing that it would actually harm them.