Agreed. People often lose their sense of ethics when interacting with companies. “Oh it’s their fault, my gain” etc. Sounds like he paid for it, it was accidentally refunded due to a technical issue, and did not pay for it again.
I’ve accidentally sent a person or two double shipments of something they bought, and when they let me know, I thank them and they keep it. Or I’ve received random test kits from BRS, called them and they said that they were replacements meant for someone else, and that I can keep them. Best to be ethical.