"Some car starts off at the red light."
Translation:Valahány autó elindul a piros lámpánál.
"Néhány autó" or "valahány autó".
The sentence above with "Some car starts off ..." is talking about a single, unspecified, car. This translation, "Valahány autó ... ", is talking about multiple cars. So, the translation is incorrect. I am not sure how to correctly translate this sentence. Maybe simply "Egy autó ..." or "Valamelyik autó ...".
The English sentence is grammatically incorrect and therefore ambiguous. I have reported it.
The issue with this sentence appears to be the translation of the word 'some'.
"Valahány" is a new word for me. It appears to mean "some" in the context of an unspecified number; except in this sentence. Here "some" does not define the quantity, but rather the (vague) degree to which the car is identified.
In short I believe the translation is inaccurate.
You believe very right. Valahány refers to "some number of" objects. A proper translation here would simply be "Some cars start off..."
The given English version would be better translated with "Valamelyik autó" - "one of the cars".