Well, it's actually four words (!), but no, he can't just get a refund by typing those in. He has to return the item to you first, and tracking has to show delivery or attempted delivery back to you. Not sure what would make you think otherwise.
Whether he's lying or not is irrelevant. PayPal can have no idea whether he is or not, as they can have no idea what you actually sent or what the buyer actually received, or what condition it was in when received, because they were not present when sent and received. They have to accept a buyer's word for it, as per their buyer protection policies.
So just agree to 'return for refund' within the PayPal case, which will put the ball back in the buyer's court. DO NOT ignore, or the buyer will be able to escalate the case to PayPal (on day 3 if memory serves), and PayPal will force the refund without the need for return.
The return will be at his expense (PayPal has no way of forcing a seller to pay return costs). When he realises this, he may close the case or simply let it time out (which it will do in your favour).
When/if you receive the item back, refund in full. And if the item is indeed not-as-described, then you should repay his return costs too, of course.
You will have been sent notification from PayPal that a case had been opened, so check your email account and spam folder.
@bunglebear1970
