It's good at determining whether something is moving towards it or away from it, but bad at determining where that object is; whether it's directly in front or slightly to the left or far to the left. Its "vision" in that sense is blurry.
Poor angular resolution means you can't tell if an object is at 12 o'clock vs 1 o'clock. It means you can tell there are things, but you don't accurately know what angle they're at.