I was about to just ask about the same.
Today suddenly about 15 games got some updates, but the download size was 0. Only one game "ATOM RPG: Trudograd" got a real update - 5GB.
Amongst these updated ones there is "Kerbal Space Program", for which I have the automatic updates turned off.
I recall that this is the second time when it happened. Or actually, it is the second time that *I have noticed* that it happened. After you restart your computer, there is no sign of any recent downloads.
Does someone know what is happening there? Has someone hacked GOG's servers (you now - out in the wilds there is that story about stolen data from CDPR) and is installing some nasty stuff on our machines?