In fact, it does not mention a difference, just both concepts Electronic confirmation receipt and then AOR. In addition, there is a definition as well on IRCC site.
Acknowledgment of receipt (R10 passed) letter
An acknowledgment of receipt (R10 passed) letter is issued to an applicant (or their representative, if applicable) once their application for permanent residence has passed the R10 completeness check. The letter is issued by the Centralized Intake Office. If the application was submitted electronically, this letter is sent to the applicant (or their representative, if applicable) via their MyCIC account; otherwise, the letter is sent by mail. This letter should not be confused with the electronic receipt of the application for permanent residence letter. This is the official acknowledgment of receipt letter and it may be used to support a bridging open work permit if all other requirements are met.