I get the impression you are expecting that long chain of if (incomingByte == statements to come into play only if you have received an incoming byte.
But as you have written the code, they are executed every time through loop().
So, unless something has been received and stored in incomingByte, then incomingByte will contain zero, and that is why every time round loop() it finds that incomingByte is indeed zero, thus prints out "Command: Turn On".