Its the 'silicones' in the hair shampoo that give the 'effect' that the car is clean
However hair shampoo is good for grease on the hair but not harsh enough for grease found on a car
Whilst you will obtain a good 'look' from using it, you will find that you need to deep clean / cut back or possibly just claybar more regularly than using a specialist car product, due to the non removal of the particles that you are trying to remove.
Whilst hair shampoo is PH nuetral the same as car shampoo, try washing your hair with car shampoo
you'll see just how much more it strips off your hair!!
The same 'silicones' are present in various car shampoos, normally the ones that 'self dry' 'gloss enhance' etc etc