No, he's either incorrect or you have misunderstood what he was saying.
Nobody knows what the car's value is going to be at the 3 year point and this is the beauty of a PCP agreement. The MGFV is a predicted value at that point.
When you get to the 3 year point, you still owe £10000. If your car is worth £9000, you would need to fork out a grand to buy your way out of the negative equity under normal circumstances. Under a PCP agreement, the Minimum Guaranteed Future Value takes car of this leaving you with either
a) A nil equity balance if your car is truly worth less than the MGFV or
b) A positive equity balance if your car is worth more than the MGFV.
Guaranteeing against negative equity providing the condition and mileage is as set out in the agreement.
So, if, in 3 years you buy a car for £30000 and your car is worth £8000, you finance £30000
Alternatively, if the car is worth £13000, you finance £27000 because you have positive equity balance.
PCP is there as an alternative to 5 year HP for those who need to be able to change the car at 3 years but cant afford payments to own the car outright over 3 years.
It is difficult to explain this face-to-face, never mind on a forum but I hope I have cleared this up for you.
Remember that all of these values are trade values. If you can afford to and, if the car is worth a good deal more and you can be bothered with the hassle, pay the MGFV and sell the car privately - achieving the retail value. Risky, yes but this is something you will have to assess at the time dependant on market trends then.
JJ