If you're concerned that someone has hacked your account, or could, you should follow the advice from Microsoft Support: Help protect your account
I did some testing and a deleted draft does indeed go to the Deleted folder. Deleted messages also seem to stay there until you explicitly empty the deleted folder. (The exception would seem to be for "child" accounts, where deleted messages are permanently deleted.)
So, if someone did have access to your account, the scenario you describe is possible and as Christian points out, only the administrators of Outlook.com could tell for sure what happened, and they're not likely to share that information. However, if someone did have access to your account, why would that be the only bit of shenanigans they did?
In any event, the advice on protecting your account is good practice whether you've been hacked or not.