This is because parallel lines have the same slopes, like in this case where they are both -4.
Perpendicular slopes have opposite reciprocal slopes, which is just the fancy way of saying different signs and a flipped numerator/denominator (for example -4 and 1/4 would be perpendicular slopes)
If it’s neither, than the slopes aren’t the same or opposite reciprocal (for example 4 and -4 or 2 and 8)
