Most themes nowadays come with their own auto-update check that buyers really enjoy, because they do not depend on the Envato Update email and do not have to go through downloading the theme again from ThemeForest.
Right now, most authors have built a custom solution where they define their Theme Version on their server and their Theme connects to their own server to compare the versions.
This is unintuitive, and an unnecessary hassle for the authors. With individual theme versions available inside the Envato API, one can easily compare the versions and then download the update directly from Envato.
My bad