@gigabarto
that's just a McGuffin a convenient way to make the MC know something he clearly shouldn't.
Who are you to say somebody can´t have knowledge outside of something they actively work as...
That's a bullshit argument if I ever heard one.
It's not like a construction worker can´t have the knowledge and skill to be a cook, or a bankier could have knowledge on how to build boats.
Just because something is outside a persons line of work doest mean they can´t have expert knowledge on a different subject...
Yes sure it's just a convenient way to give him the knowledge, but that can be done in a billion ways and you have to establish it somehow if you want the character to actually have it.
it's not that much different than just saying "oh I did construction /city planning in highschool like a "normal teenager" but did not manage to find a job so I started working for a fast-food chain.
It isnet a sin to give new knowledge or abilities to a character based on past experiences, you just have to have a somewhat valid reason for doing so.
Also, it can be done in a much more hand fisted ways than what I used as an example, but really that isn't even all that important anyway.
Without reading the novel we aren't going to know what the MC really meant to say.
It might have been poor writing in the first place where the MC was doing an asspull just to look good to the readers where he is also stupidly wrong as well.
But I was giving the author the benefit of doubt as I have not read the novel and it could have been detailed that were removed in the adaptation instead of being just poor writing.