idk, but it looks like the hacker found a bug to exploit on that server in specific.
or, the server just bugged by itself, and while the plugins and scripts wasn't properly loaded, he made some spam.
i might be wrong, but i guess that's just that.
some time(years) ago, in a 0.3b server that i used to play, something like this was happening sometimes... i crashed the server, the server restarts, but it doesn't load all the scripts(including anti flood, admin commands and lots of other stuff). And so, they had to manually shutdown the server and run it again on their VPS to make the things work again.
...so, my guess is that is just a bad scripted server(but it can also be a secret general bug in all samp server, maybe we will never know the truth about this case).