Alex, "füvön áll" means "stands/is standing on the lawn". As far as I can see, there is nothing wrong with the Hungarian sentence.
DL translates this as "is on the lawn" instead of "is standing on the lawn". It is true that "is" is not a literal translation of the Hungarian. However, when speaking of a car's location, "is" is more idiomatic English than "is standing".
So I wouldn't call DL's "is" a mistake. However, I do think that DL should accept "is standing" as well as "is".