Assuming that it is a boarding school with a dedicated college counseling staff that has insider connections to highly selective colleges of your interest, it sounds like they are saying that they believe that admissions readers at those colleges tend to see that course as lower rigor than other electives that may be available at that school. He should ask the college counseling staff whether taking that computer science course versus some other elective would significantly harm his chance of admission to his colleges of interest as a prospective computer science major.