FWIW, I've downloaded Deepseek's R1 (DeepSeek-R1-0528 -- which is released after the your linked article) model's weights and ran it locally. I asked it about what happened in Beijing 1989-06-04, and it basically gave me a stern statement that could have been written by CCP propaganda department. I asked it to give other alternative views besides the CCP perspective, but it simply continued to stonewall me.

So yeah, the model itself is tuned at least somewhat to refuse to talk about politically sensitive things. It's not just another filter.