He didn't dismiss the humanities he said studying them at university was a poor decision.

Moreover, it wasn't really presented as general advice, but advice for their own younger version. It's not generally applicable advice (not everyone will be happy or successful in STEM fields), but I think it's safe to assume it is sound advice for Young!nydwracu.

Or even if it was intended as generally applicable advice, it's still directed at kids gifted at mathematics, who will have a high likelihood of enjoying STEM fields.