Its not a DoS attack, its spamming cmds to the server causing it to lag. A recent patched one was 20 lines of rcon_password with random symbols.
Also, DDoS implies that more then one person is sending packets and trying to floor/crash the server. DoS = 1 ; DDoS = 2+
Sorry its a pet peeve when I see someone calling a dos a ddos
one more thing. Even if the steam ID is banned, you can still send commands to a server, so you would need to IP banned said person to stop them.
Luckily with the newest update, all the old ones no longer work and these 12 year olds can't mess with servers.