Security alert for someone else's GMail

I got a security alert on my phone because a friend of mine logged on to his own GMail account.

Checked with them, they were logging into their own account, but I got a security alert.

I use GMail on my laptop, & the alert was on my Android.

I shouldn't have their account as anything other than a contact. What is going on?

EDIT: Solved! It wasn't an issue with my GMail, it was a setting on my phone.