If a slamming model makes a successful slam but moved less
than 3 ˝, it has not moved fast enough to get its full weight and
power into the blow. The model makes an attack roll against its
target. If the target is hit, it suffers a damage roll with a POW
equal to the attacker’s current STR but is not slammed. These
are still slam attack rolls and slam damage rolls.
Check out the bold portion. A slam attack were the attacking model moves less than 3 inches is still a slam attack, it just means that the model is not slammed (moved) from the attacking model.