Find my on an phone that is logged out of iCloud

I’m in a situation where I bought a used iPhone that after checking it on iCloud lock checkers (that you use to check if phone is locked) it reported iCloud free & find my is ON. It’s not logged into iCloud & after checking neither is it jailbroken. Can anyone explain this situation. Assuming that I log into ICloud and activated find my, without resetting dose it overwrite the activation account in the iCloud database? And will the previous owner be able to track my activity or location? I once bought an iPhone 7 in a different situation (actually my first) it also wasn’t logged in to an iCloud account I logged in but didn’t activate find my . After updating to iOS 15 from 12 it told me that the iPhone was locked to owner. What happened if anyone can explain.