Well the confusing part is that he got his dpf clogged after 500kms of freeway driving.
Preceeding that was city driving mostly but one would think the freeway drive would help do a regen.
Yes, a long drive on a heavily loaded system can result in a trip to the dealer.
We need to find the VW theory guide on DPF to explain this. It has been a while since I read it, but basically the safety system kicked in to prevent an automatic burn.
This should be close to what happened. Read the theory guide if you want to get it 100% correct.
The system does not want the ash level to go over a certain percentage. If you do a lot of in town driving, you can go over that level.
All is not lost at that point, the system will still try to initiate a burn. A long highway trip is perfect and the burn is started. But, the computer monitors the burn temperature. The more ash you have to burn, the hotter the burn.
Once you hit a certain temperature, the system will shut down the burn.
All is still not lost. You are on a long highway drive and the system will cool down and a second burn will be attempted.
If this burns gets too hot, ie too much ash, this burn too will be aborted.
After a few burns (forget the exact number) the system will set a fault and no longer attempt to do anything.
At this point, you are supposed to take the vehicle to the dealer since you have a fault. The dealer computer will instruct the dealer to do on forced burn (forced regeneration) under controlled conditions. Not inside, not near any grass or vegetation, preferably parked over concrete.
If it is successful, you get the car back. If it fails, you get to purchase new exhaust parts.