-snip- Instead of clicking the "Preview" button, I clicked the "Reply" button and the result was fine, but the post was random and unrelated to the topic so I deleted it immediately.
Maybe you can try using the preview shortcut (alt+p) to prevent this from happening again.

I don't know if the topic remains in the administrators' trash folder, and here a question came to my mind: why isn't there a "trash bin" for users who sometimes have to delete their posts or delete them by mistake, so that they can be accessed later and either restored or permanently deleted?
Your post reminded me of this topic from fillippone:
RECOVERING the ORIGINAL version of an EDITED Post. I don't think a personal trash can is necessary, since the
drafts page already works pretty well in retrieving the full bbcode version of your recent posts.