Hi
I got the same thing this morning, I thought it was just going to be an update and it reinstalled the whole thing.
I didn't have time to sit down and see if I can tell what's different today, like if it fixed Cortana or anything like that.
I'll try and figure it out tomorrow.
The extra 20 Gigabytes on your hard drive was the Windows.old file it created during the install.
Mine is just about 20 Gigabytes too.
Mike