I agree,It also likely is carrying particles from previous vehicles trapped in the fabric - there's just no vigorous flow of water to flush that stuff off...
If you want to avoid swirl marks, never take your car through an automatic wash! Hand washing with a double bucket method is the only way. There is no way that grit is completely washed off the car wash fabric from the guy before you..
My RL is 8yrs. old and I have absolutely no swirl marks because it has never been through an auto car wash. Black vehicles won't show swirls any more than other colors if you wash it correctly. Also, make sure when you have you truck serviced at a Honda dealer, tell them to never courtesy wash it!