From the landing page:
"REMINDER: Only Aeroplan Points earned under the Aeroplan Program, the Chase Aeroplan Card, and Chase Ultimate Rewards can be used for Chase Pay Yourself Back. Points converted from other programs are not eligible. If you proceed contrary to these terms, the Aeroplan Program and Chase Aeroplan Card reserves the right to reverse your point redemption or freeze your Aeroplan Membership account."
To me points purchased from Aeroplan would count as "earned under the Aeroplan Program". This is mostly to prevent PYB from being used from Amex or Cap1 point transfers.