Tldr for those who are confused, since Android already does support side loading and even seamless updates for third-party app stores (like Droid-ify, etc), these are mostly legal changes.

Basically Google can't force Google IAP as the only method of payment in apps anymore, can't block companies from advertising how to find them on non-Play Store android app stores. So good changes overall.

Also when you download third party apks, on Android, while it's still relatively easy to do, it does give bit of a scary warning saying security issues are on the user for doing so. This creates the assumption that Play Store is the only secure way to get apps on Android, and the OS gives all sorts of special security exceptions to the Play Store for that. Obviously other secure app stores can exist, so this can be seen as an anti-competitive method since Google is exempt from their own scary apk install message.