Unknown iCloud.com account appearing while filling in a form online

Hello guys! I have just discovered one weird thing. I was filling in a form online and I was going to write my personal email. The Mac, instead of suggesting me the email, suggested one which is not mine. The problem is, the email is not of a parent or a friend. I have never seen such an email; I am the only one which uses the Mac, the iPad and the iPhone.

I wonder if this means that in some way my account has been hacked. Any suggestion how can I solve this mystery?

Thank you so much!