Attacking servers =/= spamming chat
Attacking a server, in most cases, means a DDoS attack. I don't see spamming chat as potentially threatening a server... You also happen to know someone who got all of their keys revoked, so I'm inclined to believe that he didn't tell you everything, paraphrased or he's throwing you a loop. Why would spamming be a key revokable refraction? All it takes is a ban and they're off the server. Honestly, I think you're missing kind of a key component:
after admitting that he had done it.
So had he not admitted to anything, he would have his keys. Unless you just miscommunicated?
Also, the "No. You're wrong." stuff is really annoying. Kinda like in the movies when the hero realizes he's been back-stabbed and everything is falling apart. "No! I don't believe you!" Try to have a more open mind maybe. Unless we're talking directly about you, and you know for a fact that you were banned for spamming, then you don't know either.