Required to change password after Safari 12.0.1 update. Why? For which account?

I just discovered which account password I changed. It was the MacBookPro login for my admin user account. Discovered that when prompted for my password to install a software update on my MacBookPro.

Apple needs to spell that out in their instructions -- needs to say that your iCloud account password cannot be the same as the password you use to log in to your Mac computer account. Jeez!

I changed the password in a pop-up dialogue box prompting me to do so on an installation page for the Safari update. In other words, there was the following sequence:

1. I clicked "update" on the security/Safari update link in my MacBookPro Apps program
2. My computer restarted/downloaded and installed the update
3. I log back into my MacBook Pro using the password I've always used
4. Next screen is a continuation of the installation process asking me if I want it to update iCloud now or skip and do it later (I don't know the answer to that, really, so I say Update Now)
5. Next message alerts me to the fact that I can't use the same password for my iCloud account as for some other, unnamed account, so I have to enter a new password
6. I enter a new password (and write it down so I'll have it when I figure out which account I just created it for)
7. Then my MacBook closes the installation screen and opens up my usual desktop and apps

Not sure what else to tell you. I'm totally mystified. Sure wish Apple would do a better job of thinking through the user's experience!

I appreciate your willingness to help!

Michele