Okay, looking at this, it made me think about what may actually be in the EULA for the World Editor that Modder's use. I know that somebody else already quote the appropriate section of the agreement, but I think I will again for my own points.
1. RESTRICTIONS ON USE
The Editor and any other software that is available for download from this Site is and shall remain the copyrighted property of Bethesda Softworks and/or its designee(s) and You shall take no action inconsistent with such title or ownership. You may not cause or permit the sale or other commercial distribution or commercial exploitation (e.g., by renting, licensing, sublicensing, leasing, disseminating, uploading, downloading, transmitting, whether on a pay-per-play basis or otherwise) of any New Materials without the express prior written consent of an authorized representative of Bethesda Softworks. This includes distributing New Materials as part of any compilation You and/or other Product users may create. You shall not create any New Materials that infringe upon the rights of others, or that are libelous, defamatory, harassing, or threatening, and You shall comply with all applicable laws in connection with the New Materials. You are only permitted to distribute the New Materials, without charge (i.e., on a strictly non-commercial basis), to other authorized users who have purchased the Product, solely for use with such users' own authorized copies of such Product and in accordance with and subject to the terms and conditions of this Agreement and all applicable laws. If You distribute or otherwise make available New Materials, You automatically grant to Bethesda Softworks the irrevocable, perpetual, royalty free, sublicensable right and license under all applicable copyrights and intellectual property rights laws to use, reproduce, modify, adapt, perform, display, distribute and otherwise exploit and/or dispose of the New Materials (or any part of the New Materials) in any way Bethesda Softworks, or its respective designee(s), sees fit. You also waive and agree never to assert against Bethesda Softworks or its affiliates, distributors or licensors any moral rights or similar rights, however designated, that You may have in or to any of the New Materials. If You commit any breach of this Agreement, Your right to use the Editor under this Agreement shall automatically terminate, without notice.
Your breach of this Section shall constitute a material breach of this Agreement and/or of applicable copyright and other intellectual property rights laws and treaties, and may subject You to civil and criminal liability.
Now, as I read this... this does NOT give Bethesda ownership, but rather grants Bethesda (and ONLY Bethesda) the right to do with these mods as they see fit as part of being able to use their product. A game mod, like any other creative work, is in effect copyrighted as soon as it is created, as asserted in the "Berne Convention for the Protection of Literary and Artistic Works".
Additionally, there is the sentence stating: You shall not create any New Materials that infringe upon the rights of others, or that are libelous, defamatory, harassing, or threatening, and You shall comply with all applicable laws in connection with the New Materials. THIS is something that is directly at the heart of this issue, as the author of this mod DID infringe upon the rights of the authors.
There is nothing here that states that Bethesda owns anything anybody else does. They just have rights to use anything they want from the Mod community. This does NOT grant anybody else to do so.