Originally Posted by
Jerrelle™
Hello Akio, not to be alarmed.
This is done as the user you have quoted has requested (in their own profile settings) that all replies towards messages they have posted, will have that Poster notified of someone quoting/replying to their message; this is so they do not have to constantly check the thread for replies and can be quite handy.
Unfortunately you cannot disable the notification for them, however you can enable/disable it for yourself - i.e you wouldn't get PM notifications of people quoting you, to do so just click 'Settings' > CTRL+F > "Quote" > Select 'No' to disable; alternatively you can enable it this way too via email notifications or Private message notifications.
tl;dr - this is a notification to people who you have replied towards/quoted - IF they have the quote notification setting enabled.
Reply here if this answers your question. :)
Jerrelle