This is correct. ASIAir guiding and the mount PEC run independently. If you search on other forums such as CN you will find that many users disable mount PEC since it can "fight" with software guiding, resulting in overall poorer results.
PHD2 has a Predictive PEC guiding algorithm that calculates PEC during a guiding session and automatically corrects for it. ZWO does not make this available in the ASIAir, but hopefully will in a future version.