Because of a bug on the site. Basically, if you edit your post on something that was posted a long time ago and you don't have the points to bypass moderation, the post will show up in the admin again for some reason. Then if an editor+ chooses not to approve it, it will be hidden.
Not sure if PM knows about this, should be fixed though as it becomes a problem pretty frequently with newer users constantly editing posts on moveset threads and stuff.
EDIT: I just looked at the post and approved it. The images are gigantic which is probably why they were hidden, the page lags enough without extra images to load.