That is likely because you have added your MicrosoftID (outlook.com account) to your tenant's directory. MicrosoftAccount is the identity provider linked to such accounts, and federated basically means, that an external identity provider (external to Azure AD in this case, not external to Microsoft) is responsible for authenticating this user. Here's for example how it looks for one such user in my tenant:
Refer to the following article for more details: https://learn.microsoft.com/en-us/azure/active-directory/external-identities/user-properties