My phone (Lumia 1020), running build 581, just found an update. It downloaded quickly, restarted the phone, migrated data, etc. Phone's back up but the build # is the same. Did this happen to anyone else?
It could well have been 10MB. The download was quick but it still went through the reboot, gears, migrating data, etc. Phone is working so I guess it's not worth trying to figure out, especially if a few others have seen a similar phenomenon.
Yes, I think most people had this happen to them at some point after the 10581 upgrade.
There are other updates happening in the background that we do not always see. Apps, especially, seem to be updating to keep up with the Preview Builds.