Perhaps, because the thread still exist in the Forum? It is possible to setup a "Papierkorb" (German Name) for moving deleted Threads inside smf. Therefore a Post only moves to this place, when a posting would be deleted
I guess you mean a "Recycle board". Yes, SMF has this feature, and I use it myself
. If you're wondering about it, go to the "Settings" tab in the "Boards" option in the admin panel, and choose a dedicated board for "Board for recycled topics".