If you're shortening a link from a website that uses Bitly and you see it shortens to a different domain than bit.ly or your custom domain, it has been auto-branded.
Auto-branding is a feature that our Enterprise customers use to automatically add their custom domain when a link to their websites is shortened.
For example, if you were to shorten a link to this page on your free Bitly account, instead of bit.ly/******* it would be auto-branded to bitly.is/****** since Bitly's custom domain is bitly.is.
However, you can edit that link and revert it to bit.ly/YourEditedLink/ instead of the custom domain with /YourEditedLink/.