Yes, that is correct - the @sky.com domain was the likely cause. It means there is already a tenant setup and using the @sky.com domain. This would probably be Sky itself.
You would either 1.) Log into Teams with your corporate address (I.e. email@example.com) if you are using a paid version of teams (I.e. Office 365) 2.) Log into Teams with a email address such as hotmail.com, outlook.com or gmail.com) if you have signed up for the Free version of Teams