It's the ARRF commander's decision on what he calls out for the emergency. My guess is that he expected a normal landing, but was prepared for the worst. Not too much cost to roll the extra manpower. They probably appreciated the chance to exercise the equipment and get out of the ready room for a while as well.
Besides the same Monday-morning quarterbacks (like dimwit blondes on the network morning shows) that would criticize him for bringing the majority of the brigade to the fight would also crucify him if something bad happened and all the equipment wasn't there.