This is only with FSDT add-on added, no special AFCAD just whatever came with the product. This has happen a few times.
First, check if GSX is really using the FSDT AFACD, this can be verified by opening the parking customization menu, that will list the name of the AFCAD in use.
So is this normal? I thought the car would follow the AFCAD.
No, it's not. The car obviously follows the AFCAD. If this happens with the AFCAD supplied with the scenery, please indicate the destination gate you requested and the position you where when you requested the Follow Me car.
If another AFCAD was in use, please indicate its name. However, if another AFCAD it's in use, lots of other things wouldn't work in GSX, such as docking systems and our airport customization.
Also, does GSX update its airports database (or whatever it is using), every time I check or un-check an add-on airport or scenery to keep current or would I have to restart P3D? I am using P3D.
It not needed to restart the sim, P3D doesn't make any difference, and in any case, you can also restart Couatl with its own menu.