Does gaps caused by backlogs are also considered as gap year?

If a 3 years course is completed in 5 years, it will not be considered to be a gap. However, it will become quite apparent that there have been backlogs which might hamper the chances of getting shortlisted.

Gap year is gap taken between your studies. Your friend did not actually take a gap, I assume. He just took time to clear his backlogs.