1) He said he couldn't fill a request to have his stuff sent back because the form was broken. It's very believable if you ever used the amazon seller tool.
2) He submitted the evidence of authenticity and it was rejected for being older than 365 days. It shouldn't be a problem, clothes have a longer shelf life than one year.
3) Customers complain about products being unauthentic all the time, easy way to get a refund and to vent. It's the most generic 0 star review that can come up possibly from a competitor trying to damage your business. You can't sell a thousand items without getting a few bad reviews.