Almost. The author can license their contributions with a more permissive license if they want (e.g. individual files can be MIT licensed) but the software as a

Almost. The author can license their contributions with a more permissive license if they want (e.g. individual files can be MIT licensed) but the software as a whole must be licensed under the GPL. I guess it boils down to whether the LICENSE file is meant to apply to the code in that repo or the software it produces when built. I would expect the latter, but I guess it's a bit ambiguous since we're having this discussion.