Updated password in keychain was reverted

Hi,

When my MacBook is being checked for errors by store technicians (apple certified warranty center) (which logged out everything including iCloud and erase all contents and settings and reinstalling macOS), I updated (manually) several passwords on keychain by my iPhone. All the changes were saved, but when I got my Mac back and logged in iCloud all the changes were reverted back to before. I felt like it can be a copy of my keychain and passwords were saved on the Mac when I brought it to the store and when I logged in it update the copy as a new version. Can it be the technicians do this on purpose or it is some kind of malware that were used to extract my passwords?

Thanks for the help