2. flies to Cuidad del Este and takes a walk towards the bridge. He does not stop at the Paraguayan border office BUT he stops at the Brazilian border office (no exit stamp from Paraguay)
Why would the Brazilian border office give you an entry stamp into Brazil if you don't have an exit stamp from Paraguay? In most Latin American border crossings I know of, they would tell you go to back and get your exit stamp before you can be stamped into the country.