You aren't allowed to just read code and regurgitate it in order to claim it as your own. That is, just because you memorized this great new novel you read, it doesn't mean you can go and sit down and hammer it out and sell new copies. People go to great lengths to do this sort of things (see: clean room reverse engineering [1]) in order to try and wash themselves of liability.
[1] https://en.wikipedia.org/wiki/Clean_room_design