He won't be notified, and he won't receive it in his "Messages" inbox. This is just a plain Public message that happens to have the word "sazius" in it."
I wrote that message at work, between lots of different activities plus I tried to emulate manually what application can easily automate. Struggling with Pump.io blindness to Comments on Comments... :-)
And naturally I forgot to send the composed message as a "reply".
This is a piece of cake to parse message for @username@hostname (or even for "Display name" of some favorited recipients...) and add them to "To" field. But this effectively frees a User from having that "To" field at all.