Criminal law, "beyond a reasonable doubt", doesn't mean "there exists, however implausible, an explanation".

He did break into the network - he was spoofing MAC addresses. You don't have a level of technical sophistication allowing you to do this, and then say "oh, I assumed the server closet with an "Authorized access only" sign, usually locked, seemed like a safe place, that's all, and since I was there, I figured I might as well just plug directly into a network switch in there."

Many judges are not technical. Most judges are not idiots.