OK, I just tested it a bit and the WHISPER thing is actually something my bot does and “converts” into the PRIVMSG like stated in the post you linked above.
My bad, sorry for the confusion.
This just worked to send a whisper from my bot to myself:
PRIVMSG jtv :/w TheRealHellcat Testing.... 1, 2, 3
Note that there’s no “#” in front of the “jtv”.
//EDIT
Aaand I figured again where the “WHISPER” came from. When the bot receives a whisper, it’s sent to it like that…