Hi @LinetteC,
While I don't know every situation that would cause that message to appear in the quiz log, I did want to point out that Instructure's official documentation on the quiz log says, "Quiz logs should not be used to validate academic integrity or identify occurrences of cheating."
I can imagine that perhaps a system (windows/mac) notification could pop up on their screen and just closing that technically means the web browser doesn't have focus for that split second. If they are on a mac, they could have gotten an imessage and wanted to check if it was important/urgent. Now granted, you may tell student not to do that and may choose to deduct points if they do, but there are probably a multitude of similar scenarios that students could run in to.
Overall, I'd really just recommend sticking to Instructure's recommendation and not using the quiz log to try to identify cheating/academic integrity issues.
-CHRIS
