What is the error when inserting the script?

Question

Burglary protection

Bet with a friend that I would find a hole in his site.
This is the situation: I enter in the field to send a message, and I get ';!--"=&{()} as output. It's clear that the site swallows everything in brackets. But after that, when I open the HTML code of the page, I don't I can find my fuck. (I searched using the F3 button) Please tell me what I did wrong, is the site vulnerable or I'm not catching up . !! '';!--"<fuck>=&{()}