Faulty part return

Dell Assist diagnosed a faulty hard drive(HDD, not SSD)  for my XPS 8940 and Dell sent out a tech with a replacement.  All fine and great there.  However and this is problem - The tech asked if I wanted the keep the old drive and I said yes.  I wanted to see what if any data could be recovered.    He left me the drive and the mag wrapper, took the box the new came in and left. I got an email about the completed repair that was under warranty (PC is less than a year old) and found this notice :
Customer acknowledges and agrees that Dell owns all parts removed from the system. Customer confirms that if they retain the parts temporarily they will return the defective parts(s) within 10 days from the completed date stated in this form and in accordance with Dell's Terms and Conditions of Service and Support. Customer agrees that if the Original Part is not returned to Dell within the agreed time frame, an invoice will be issued to the Customer by Dell for the value of the part at Dell's current price and Customer will be liable to pay Dell this amount invoiced. If Customer holds a Dell extended warranty service that permits the retention of specified services parts, such as the Keep Your Hard Drive service, the terms of that service will supersede the Customer obligations described in this paragraph, and Customer will not be invoiced for the relevant service parts not returned to Dell within the agreed 10 day time frame.

The tech NEVER mentioned it had to be returned and did not leave way for it to be returned.   The work order shows I have Additional Offerings - Keep Your Hard Drive(KYHD).  

So do I really need to return it?