Because the only reason he got in was because of the RAT, once he removes it and resets router so he hasn't opened ports etc, changes passwords etc what other threat is there? He didn't get there by hacking into the router, he got there by a piece software that allows a remote "operator" to control a system as if he has physical access to that system. Its like working from the inside out, Yes he could have found out all his passwords, open ports etc but by changing all that, there isn't a problem.
..that is assuming it is an RAT and he is correct, but either way it will work what ever it is.
