Listen, there are so many legitimate criticisms of Reddit, no one needs to make things up. This happens every year in June. Somebody posts about Tiananmen, some automod or real mod removes it, someone screams "Reddit" is censoring things.
There are tons of posts about Tiananmen that are still up after years. Tencent owns a small minority stake in Reddit.
https://www.reddit.com/r/China/comments/gvwu6h/megathread_tiananmen_square_massacre/
https://www.reddit.com/r/HongKong/comments/gw2y6b/the_real_picture_of_tiananmen_square_massacre/