What grade did he earn in the course?
If he earned an A in the course (and previous math courses), that can be a warning that the high school’s courses are not of good quality, or the grades are highly inflated. He may need to review or learn any gaps in his knowledge of high school math before going to college to study engineering, regardless of what SAT subject scores he presents for admissions. Otherwise, college math and everything depending on it in engineering could be a difficult struggle.
Many colleges will have math placement tests like this one that new students take before enrolling in calculus 1: http://www.math.buffalo.edu/rur/rurci3.cgi