Using login in credentials that are not your own found in a public place to take source code is like finding someones house key on a park bench and coping their secret invention designs or trade secrets.
As I read it, he didn't use the credentials to take the source code; he found the credentials in the source code. He used the credentials merely to verify the credentials were valid.
Define "take" source code. Do you mean "read" or "access" source code? I know this is an aside, but I think we as a community need to be more judicious in our use of criminally-accusatory words, especially when it comes to taking/stealing/theft vs copying vs distributing/selling vs reading/watching/accessing. They're all very, very different things.
You read my post in the ~5 secs widow where it had the word "take." It was the wrong word because in the case I was talking about it would not have deprived Prezi access to their source code.