is there another person's apple ID account associated with mine?

I still have a gmail account as my Apple ID (from forever ago) but I have also had an @iCloud email address for 10+years which is my main email. I used to be able to login to iCloud & Apple.com with my iCloud email address and password, but now its not working. I can login with my gmail Apple ID, but im confused.

when I look up my Apple ID under the "forgot Apple ID" link.. and I put my information in, it shows that my Apple ID is my @iCloud email, not my gmail. but when I try to reset the password, the security info doesn't match mine. the "associated" email is not mine, and the birthday question doesn't match.

does this mean someone else created an Apple ID with my @iCloud? if so, can they access my email account?