My chemistry is nowhere near good enough to evaluate the claim. And scientists do get it wrong but I think he'd likely know. And it makes sense. They're not using it to make an abrasive soap, they're using it to make a surfactant. Which is liquid, not solid AFAIK.

That's not to say the product won't still be problematic, but possibly no more problematic than existing surfactants used to make soap.

I don't know, and I think your general concern about releasing things that were once plastics into the water supply is reasonable. But the plastic is going to end up polluting the earth in one way or another, in one form or another. At least they're using up the old stuff not generating any new.