Here's what went down

On the morning of travel, TP said they couldn't print me a BP for SFO-YVR and the bag tag spat out AC8847. I asked TP for help at the TP service center at LIS and the agent showed me in her system AC8847 showing as operating and said she couldn't do anything. I then called AC who said I was booked on AC569.

At SFO, I lugged my bags to the AC desk, where a bag tag for AC569 was correctly printed out and given a boarding pass with seat "SBY". The agent insisted I had to get a seat assignment at the gate "because you didn't choose one in advance".....sounds made up but ok. At the gate they told me I was selected for being downgraded to Y because "you booked today and the system shouldn't have accepted your booking". I flew to YVR in Y. They did not offer any compensation at the gate but said AC would give me some if I contacted customer service even though it's a TP ticket and flight since they are the operator and they are downgrading me, but I'm not sure if they just said that to get me to go away.

Wouldn't this qualify for EU261 downgrade compensation as it's a TP coded flight and ex-EU itinerary? Who would be responsible, AC or TP?