Are we sure that are actual people and not some random bots? and anyway i think the mods must know what is going on the IRC because if continues it can harm.
It weren't the people who said this. This was officially written in the channel info by some mod/admin. The mods know about this and they must have had a reason to write this.
Then if what you are telling is right there 2 possibilities.
1) One of the mods/admin account got hacked and because of that the message appeared
2) The IRC channel staff becamed supporters of XT and refuse to consider Core as usefull but as a malware (On this one i have my doubts)
But from when is so anyway? because if is from a short time the first possibility is plausible otherwise if both my theories are wrong i don't know why (At the end Bitcoin Core doesn't have any kind of virus i suppose otherwise who knows)