Yes, the ISO is 4 GB but the Media Creation tool needs 8 GB because it will extract to the C: drive all of the files of the downloaded ISO (which is also downloaded to C: ) before copying to the USB...

Just wanted to add that you can download the ISOs without the need of the Media Creation tool, which requires you to have 8 GB free on the C: drive, and doesn't work if you don't, even if you have...