That ~15 miles/day of riding that he mentioned (1000 miles over the last 2 months)? The 500 calories he added would be about right to cover that extra burn; for most people cycling burns between 25 and 40 calories per mile, or around 375-600 calories for his mentioned daily riding.

I'm hardly an authority on the subject (read: I just did the maths after looking some stuff up in encyclopaedia assuming that burnt values per mile you gave are correct) these numbers work for 6 pound loss for pure fat that has a caloric value of 9000kcal/kg. Adipose tissue on the other hand is roughly 7700kcal/kg. You seem to be using the first value as in:

  600 kcal * 60 / (9000kcal/kg) = 4.00 kg = 8.80 lbs
  375 kcal * 60 / (9000kcal/kg) = 2.50 kg = 5.50 lbs

lost weight in 60 days (hence the 60 in numerator) is closer, and with much lower range, to the value klein reported. However, for adipose tissue it should be (again, I'm taking this from PWN encyclopaedia):

  600 kcal * 60 / (7700kcal/kg) = 4.68 kg = 10.29 lbs
  375 kcal * 60 / (7700kcal/kg) = 2.92 kg = 6.42 lbs

Again, I am in no way qualified and any corrections would be much appreciated. Not to even mention that I'm uncertain if I got the meaning behind the quote correctly. Either way, as far as I am aware for now, klein's reduced weight is pretty consistent, although in the lowest quarter for both ranges, with these values. Depending on the method of measuring the weight and its accuracy on top of that. I'll end it by saying that if thermodynamics taught me anything, this model is too broad of an approximation. Klein is not an isolated cylinder after all ;).