Itunes iphone ios update file and download

I wanted to update my iphone's iOS from 26.0 to 26.0.1 via itunes, and it was re-downloading 26.0 at 9gb+ when the update is 500mb-ish according to the iphone's own software update.

My question is why is itunes re-downloading 26.0 for a small patch update? I decided to just use my mobile data to download the small update within the iphone itself that took maybe 5 minutes with a 2 bar connection...instead of waiting 70 minutes to download 9gb+.