Where are you located? When honey bees work livestock feed they are searching for a powdery source of protein to feed to their larva. It is rather late now for honey bees to go into gang buster mode and start raising mega amounts of young brood. But if natural pollen is in short supply then anything is possible.
Trying to capture a wild hive at this time of year is a death sentence for a bee colony because they will be unable to adequately prepare their new digs for winter before bad weather hits.
He's in Arizona,
Yeah, it's a death count if harvesting wild this time of year in the north of North America. And I agree that something is up as to them being attracted that heavily to feed mash as they'd not even start a new brood in a dearth. I think it's a local hive that's using his mash feed as brood feed due to being so close.
The neighbors hives that disapeared are likely very near and even in the walls of someones shed.