There are a couple of problems with his story.
First, Amazon denied it was due to comingling:
"I’m just calling to inform you that there were no other sellers of that item that were in the co-mingling program"
Second, he apparently didn't show up to the lawsuit and had a judgement by default. Never a good sign.
Third, he was moving hundreds of thousands of items, but couldn't afford a lawyer?
Fourth, he cites as evidence that his items were comingled the fact that his returns came from a different warehouse than he sent them to. As someone who regularly sends items to FBA warehouses, this is bullshit. Amazon sends your own inventory between their warehouses, and you can track this in reports. Often I send to warehouse A, and it immediately goes to my reserved inventory, and then it goes to another warehouse a few days later. Anyone who doesn't know this didn't invest enough time to learn about Amazon policies, and you should doubt their story.