It doesn't make much sense in Hungarian either. This is more an exercise in grammatics than reality. Your translation is not equivalent, saying "the car is not there" is different from "that is not a car there".
I can't quite grasp the sound on the border of the words 'egy' and 'lány'. Is there any special sound for the case of 'gy' going before 'l' or is 'egy' pronounced the way it would without the subsequent 'l'?
No, different meaning. Think of it this way... "There is something there. I think it's a car, maybe it isn't... Oh, that is not a car there, but a girl." Your translation misses the "location/where" of the Hungarian sentence.