Not just strange.  Fraud.  Its the overpayment scam.  The scammer is an idiot.  Usually its run on a larger, more valuable item, like a car or a piano.  

The way it works, the scammer pays your asking price for the item, sight unseen.  You get a receipt from Paypal that the payment is your account along with some extra to pay the shipping firm.  You forward the overage to the shipping firm the buyer selected.  Paypal then tells you that your account is overdrawn.  The receipt was a forgery.  You have to pay Paypal the money you sent the shipper.  The shipper and the buyer (probably the same person) vanish.  They keep the shipping fee.