To be fair to Hiroki and his mom, I think asking a high school student to make a decision that supposedly affects the rest of their lives is unreasonable in the first place. If you had asked me back in high school to choose between STEM and humanities, I'd have probably picked humanities, even though I'm in STEM now. Deciding factors for me were things like what teachers I preferred, what courses my school offered, etc. None of those things would matter in the long term once I went to college, so they'd be bad reasons to decide too. I guess in Japan, their education system is oriented so that this decision does matter and you're expected to be able to decide for yourself what is best for you by then, but high school me certainly couldn't do that.