Awesome, thank you for clearing that up!
EDIT: Actually, I just bought the bundle and itch keys are not included. Instead they offer a download link from humble bundle. So I think you may have to update with them as well to give the bundle owners the update. There does not appear to be a way to connect the humble purchase to itch.io.
(For the record, most of the other assets also come as a single download. It looks to me like only 3 of them come with a key to register on another site/resource. So it seems that the standard for Humble is to offer a downloadable zip directly instead of an itch.io or other site key.)