Correct. But that’s not really relevant though.
Hacking is … more of a colloquial term because it encapsulates everything within IT security and data breaches. This would go under the IT security portion as it attacks the stability of the servers.
Lots of hacker groups have done DDoS attacks just as a way to get people’s attention. This isn’t something massively complicated as this could be a group, it could be a singular troll, it could be someone who paid others, or … basically any combination of these or other things.