If you remove that sentence, nothing indicates that you can see you picked the door with the car behind it. You could maybe infer that a rational contestant would do so, but that's not a given ...
I think if you mentioned that to a human, they'd at least become confused and ask back if they got that correctly.
A reasonable person would expect that you can see through a transparent thing that's presented to you.
That it doesn't, that relentless stupid overconfidence, is why trusting this with anything of note is terrifying.
Would you have this objection if we for example perfectly copied a human brain in a computer? That would still be a machine. That would make similar mistakes