It doesn't make any sense to get snippy about your question being unanswered when you mistyped it (rather significantly). You expect us to do you the courtesy of taking the effort to re-answer a question that we already answered (which I will do), so please also do us the courtesy of being polite about your request.
OK we have two definitions of Newtons first law which we would like to apply to this situation:
A) "Every object remains in its original state of rest or uniform motion unless it is acted upon by a net external force."
B) "If observation is being made from an inertial or non accelerating frame of reference , then every object remains in its original state of rest or uniform motion unless it is acted upon by a net external force."
In all reference frames the block is affected by the following two real forces: the weight of the block directed vertically down, and the normal force from the floor directed vertically up. These two forces cancel each other out in all reference frames, for a net force of 0. In the car's reference frame the block is accelerating horizontally at a rate of -a.
Definition A fails because the block is not staying at rest even though it is not acted upon by a net external force.
Definition B succeeds because the observation is being made from an accelerating frame, so the remainder of the definition does not apply.