Plenty of takedowns include lifting your opponent up and bringing them down. How you land is on both guys, not just the guy attempting the takedown/throw/slam.
Since TS didn’t post a gif, but one image and several links to twitter, I won’t rewatch how it happened, BUT I think it was a part of Edwards not tucking in his chin, not rotating through with it and having his other arm kind of stuck.
These situations happen fast and you don’t have time to think it through. You react on instict and it seems like Leon was half asleep here? I don’t know.
Those calling this an ”evil move” or illegal or something, go watch DC fights. I remember him slamming multiple opponents like that, Barnett and Gustafsson for example. They reacted much better (and didn’t have their arm trapped/stuck?) and landed just fine.