Nope. They were CC BY-SA 4.0 from the beginning. Site logs show the initial submission was set to CC-BY-SA 4.0, not CC-BY initially, then changed later. Confirmed by Archive.org on their very first snapshot of that submission: https://web.archive.org/web/20210423082200/https://opengameart.org/conte...

EDIT: clarity.

Other submissions are too recent for archive.org to have a snapshot, but the only other one with a license change shows you made two revisions, one where you note changing the license from "the wrong license; CC-BY-3.0" to something else (Site logs show it already had CC-BY-SA, but you added CC-BY as well) and another where you change the license again; "removed SA license" (instead of both CC-BY and CC-BY-SA, you removed the -SA and left just the CC-BY) so the total timeline of licenses on it is:

1. CC-BY-SA 3.0 (initial submission)
2. CC-BY-SA 3.0, and CC-BY 3.0
3. CC-BY 3.0 (current revision)

I should also note there is no mechanism for the site to change licenses on its own. Both you and administrators could change the license, but there is no way to do so without the revision log recording who made the change, Admin or otherwise. In these cases the revision logs indicate Emcee Flesher is the only user who made revisions.

P.S. Although Admins can change licenses on submissions, we do NOT do so. Even when the license is incorrect based on derivative chain, we only mark it as a license issue and allow the submitter to explain and/or make that change themselves.