Let me get this right. Little kids, harassed parents, parents tell the kids to do something, kid dutifuly obeys and you're still looking for a reason to criticise or find fault with said parents?
I'd pretty much assume that if the kids did as asked, that the parents have the discipline down pat. I don't think you'd be able to make an assumption that they dont praise ever based on your teeny microsecond glimpse into their lives. I praise when its appropriate and we have the time. But perhaps a fraught day out with lots of kids in tow wasnt the appropriate time, particularly if its clear they are being judged by complete strangers.