I don’t follow what you mean or meant.
It means he didn’t do the math right.
The PSI is the pressure as measured by a gauge, above 1 atmosphere - instead of the absolute pressure which is what is needed for the equation.
To properly do the calculation, you need to use 27.2 instead of 12.5, as 14.7 + 12.5 = 27.2.
Thus the change in PSI would a little more than double what was calculated in that example.
“I dont follow what you mean or meant.”
His calc is incorrect.