Some small hotfix (Or some such.) downloaded and replaced the game exe and one of the base ini files.
Unsure about trainer compatibility (Trainer shows as updated today so it might be compatible with this latest version already but the editor was updated yesterday so it might need to be updated again for compatibility this little fix.) and I don't know what this small update was for.
I'd assume it's some last additional fix or other issue with yesterday's big patch since it's mostly just a update for the game exe. (And yesterdays patch also added DLC compatibility so hopefully there won't be a need to update the trainer yet again on the 16th when that additional content is released.)
EDIT: From the Steam forums it was mentioned that this adds the achievement support for the DLC.