Some people sell things and give the original receipt as proof of purchase to the subsequent buyer.If the eBay transaction is fine (think the necessary time to claim will have ended by 7 weeks and no comeback) I can’t see there is anything fishy. Just send the receipt it’s not like you need it unless you do (taxman etc).
I doubt he would want to claim he’s you or that he lives at your address. If Mavic do wish to help him, then fine, if they don’t, then you’re still fine. ¯_(ツ)_/¯