Remember if something is likely to happen, then it is NOT significant because it should have happened. It is significant if it is not likely to have happened but did. Think about if I see a car drive down the road, that is not significant because that is normal. However, if I see an elephant going down the road, that is significant since it should not happen.
In this case, the original difference of means of 4 is likely so this would not be significant.
