I think the US agent is mistaking the use of the term push. Generally it means that the canceling airline has sent the info to your new ticketed airline.

If the ticket was never pushed US would have zero record of you. These days it is all done electronicaly. Since you checked in and had a boarding pass obviously US had you in their system. I'm willing to bet someone on the US side became confused by your ticket and might have not boarded you because of it.