Yes, but GP never claimed they're equal - instead the claim is that seeing the animal alive and talking to its seller to get more info is a better proxy to judge those things you listed (healthy, sanitary) than Whole Foods' endorsement is, the reliability of which over time depends strongly on their financial status, management ethics and a number of other variables outside your control. The Whole Foods approach is definitely more convenient for the buyer, at the cost of assurance.

Also, it's going to be a lot more difficult for a street-side vendor to cheat you compared to a behemoth like Whole Foods with deep pockets, the latest and greatest preservatives etc at its disposal to make meat look healthy, and a large, existing customer base that implicitly trusts its products.