You can be concerned about being popular and trendy without being superficial. Ignoring fashion, style, and appearance standards can hurt your life chances and your relationships with other people. In societies where popularity and trendiness signal and enhance status, it's rational to be concerned about them.
If your worried about your "life chances and your relationships with other people" based on fashion and style, then you're superficial, and those are superficial relations (and a superficial career).
Not caring about "fashion and style" doesn't mean you're some hobo style slob (which would indeed hurt your relations and life chances for non-superficial reasons, e.g. because you smell and wear shorts at the office).