Google Drive-unshared file access

I recently created a folder (let’s call it “A”) not shared, added a subfolder “B” and shared with two people “editor” access, then added 3 folders and a file under “B”.

One user said they accessed Subfolder “B”, but then was able to access a file within my unshared folders. Is this possible? Also, anyway to get a change list of the files or folders in subfolder “B”?

Thank you

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Author: user248569