IRC is Internet Relay Chat.
All Messages in IRC are bridged to Discord and the Minecraft Server.
Dakto INC has an IRC channel for an easier way to discuss:
Channel: #daktoinc
Network: irc.esper.net
How to tell whether a message is from Minecraft or IRC?
Minecraft chat will look like "<dakbot> %name% » example" while IRC will look like "[Discord] IRC: <%username%> example". IRC chat is only connected to Discord and Discord is connected to Minecraft so IRC chat shows on Minecraft via Discord. You can see whether a message is from Minecraft chat on IRC by seeing if its from a bot called "dakbot" which is the bridge for Minecraft and IRC.
What IRC Client would you recommend?
I (Dakto) mainly use AdiIRC Client as its free and easy to use for Windows. If you are not on windows or do not want to download an IRC client then you could use IRCCloud which is a website for IRC and a free mobile app. Another good IRC client in case you are using Unix or MacOSX, is HexChat. It is highly scriptable with Lua, Python and Perl. Translated in multiple languages, fully open source and actively developed and an easy to use, customizable interface.