Ran some tests - This behaviour happens whether I copy the bitmap image to the clipboard or not.
However it does not happen if I use the menu to capture the screenshot but only when my hotkey of Ctrl-Shift 2 or the default shift-printscreen to capture a specific region triggers the notification.
The shortcuts for printscreen for current monitor, ctrl-prtscreen for everything, Alt-printscreen for window do not trigger it the notification popup.
Notifications on my phone already show up on the computer but for whatever reason this selected region (which i use ALL the time) triggers this notification.