I took a look at the admin logs and it shows the admins/mods have not deleted anything:
That screenshot was taken two minutes ago from this post. The names of admins and other users have been removed to protect the innocent, but you can see in the action column no admin has deleted a post. The one topic that says “Deleted by author” was a post by that same author just asking if he had the permission to post; it appears he answered his own question and so deleted that post on his own. Other than that, no post deletions in the past 48 hours.
I see no setting in Discourse or your account that would prevent you from deleting your own thread, but have gone ahead and deleted it for you.