Yes that is my guess too. Because you cannot have a temporary PR visa and trv at the same time. It’s redundant. But is it confirmed? Was it in official website of Canada?
This is what happened to my partner, he was back home when his PR got approved and once he landed in Canada with his COPR, he was informed that his ETA was cancelled.
There's no direct answer on IRCC websites, but this is the closest thing I've personally found - https://www.cic.gc.ca/english/helpcentre/answer.asp?qnum=1184&top=16
You're really complaining because you have to pay an additional $7 for the ETA?
ETA was cancelled - correctly.
Applicant didn't land within the time period specified in the travel documents - so COPR expired. Correctly.
ETA is online app, usually processed quickly, and costs $7.