That is what I thought as well.
While the rest of the quoted material is fine, this is the important part. When there is a lower level of CO2 (i.e. CO2 is no longer being injected, or a lower amount is being injected) present in the water column.
With less CO2 being injected, the pH will not decrease as much, resulting in an "increase" in pH (rather, the pH shifts back closer to the initial value before CO2 injection).
Is the effect less if you have a high GH and KH?