Right: you retain ownership, and grant X certain rights to the content. Whether those rights include training AI on the data is legally and morally in dispute. X claims that right in its ToS, but a ToS isn’t law and may be legally invalid, and besides that the ToS system is famously broken in the US. Morally, I think it’s pretty clear that reasonable users did consent to their content being published as a tweet, and did not consent to X recreating the content as their own and taking credit for it.