As per the image attached, when I'm logged into my portal.azure.com (not my IUR version with microsoft account) ... this is the one where I'm logged in using my Office 365 tenant (i.e. Work Account) some of my clients are listed in my drop down menu on the right. I'm not sure hey they got here, or how to remove them. None of these have active Azure Subscriptions and I have not added myself as an admin on them at all. I've got no idea how to remove these. When I login to portal.azure.com using the global admin login for each of the clients, I can see now way to even add admins where there is no subscription, let alone remove my account from them. Also, none of these customers have ever had an Azure subscription. Hoping someone can help.
Have you shared anything with them from O365? If so, that could be causing this behavior.
Azure AD automatically creates directories for accounts in domains as needed. If those firms ever decided to use O365 and/or Azure, they will take over admin responsibility of the directory. Until that happens, MS manages their directory automatically.The UI may be showing you those directories.