Yes, a crime is a crime, but if we are going to build analogies with real world crimes they should at least be correct.
Obviously many DDOS attacks are not carried out by volunteers. They are instead vast hijacked zombie farms under the control a few people. In those cases the term "attack" makes more sense. From my understanding this DDOS attack was carried out by volunteers though. It should really be considered a protest.
What if this guy was part of a real world flash mob that formed in front of a Koch's HQ? Suppose the mob was so large it made it difficult for legitimate employees and/or clients to enter the building? He still might have been arrested but I'm sure the punishment would have been less severe.