The error of the code using Analog Pin 2 and the picture showing use of Analog Pin 0 has been discussed in another thread/error-report, but this isn't about that...
My complaint upon reading this Tutorial is that it doesn't explicitly mention that the calibration process is entirely predicated on the sensor being manipulated during the calibration period to force it swing to its boundary values.
Without this critical procedure, the maximum and minimum values lie around the ambient, unexcited range of values produced by the sensor during the calibration period. Then essentially all subsequent reads of the sensor value scaled (squished) into this very narrow range, which is clearly incorrect. In the worst case, one is left with a calibration range which is entirely unable to detect changes in input after scaling if the ambient value drifts during use of the sketch.
The tutorial needs to point out that someone must manually cause the sensor to run through its full range of possible values manually. It should explicitly state that during the five-second calibration period the sensor (a photoresistor in this case) needs to be exposed to its highest and lowest exposure values that are expected in practice. At the minimum the reader should be instructed to at least cover the photosensor similarly to how it would be covered in its expected usage scenario.
As it stands right now, I'm afraid that the existing example is really confusing.
I'd recommend that text to this effect be added to the explanation of the theory of operation, as well as perhaps a message in the code like
Serial.print("Please manipulate the sensor input so that it is exposed to its minimum and maximum expected values during the calibration period.")