Sharing Power BI Dashboards - External Users

With Power BI Premium, yes you can share with anyone, it is focused on sharing with users in your own organisation/tenancy, as with Premium, you can allocate those users with Power BI Free licenses, so they act as 'Read Only' users. It saves the expense of allocating a Power BI Pro License to consume reports. For users external to your O365 tenancy, you can still share in a few ways.

1. Create a user for them in your active directory so they have to log in with a '@yourdomain.com' email address. They are allocated a Power BI Free license and can be allocated to the relevant workspace or app.
2. Add the external user as an guest to your domain. This way they can log into using their '@theirdomain.com' email address

With option 2 the guest user will have to use your tenancy id in the url, they can't just go to app.powerbi.com as they will be logging into their Power BI tenancy. It will be something like https://app.powerbi.com/home?ctid=1234f5f6-12f3-4567-8ab9-123a456bc78d . With the guest user, you can allocate them a Power BI Free, or if they have one allocated to them in their domain you don't have to. (You don't have to have Power BI Premium to use this option, you can allocate them a Pro license if you wanted to, or they can bring their own.)

There is a third option under the licensing term of Power BI Premium, is that you can used Premium as a backend to your own website that hosts Power BI reports (App owns data), like you can do with Power BI Embedded. You have to build you own website that surfaces and handles reports access, so they don't log into Power BI directly, just your website that sits in top of it.