I don't understand, OP, context? I don't see how it's immature, did they see them as bad courses or something? I've never heard of a stigma against science courses, unless you're talking about social sciences or something. Which courses did they laugh at?
Maybe they saw how much of a joke some courses are. Employers can tell when you're taking fluff courses to pad your average. If you are trying to get into accounting and have a course on music theory 101 or something equally irrelevant they will ask why. The student will come across as having a lack of work ethic as they just do what is expected of them and no more.
7 here. @8, Oh for sure you can explain that to the recruiting officer and I am sure they will understand. I meant for those that are taking something totally irrelevant to their interests and their respective career field. There is nothing wrong with being curious regarding another subject and wanting to expand your skills. It is the people that are taking program A, have an interest in program B, but are taking a class in program Z because it's easier and will give them a higher average that any prospective employer or graduate program will look at and question.