Mysterious pop up/dialog box appears on desktop during startup of MacBook Pro then disappears quickly

I don't really have a question for the Apple community but maybe a solution to the above as I've seen a few posts with something similar. Over the last few months I've had this pop up appear on my MacBook Pro during startup but it disappears so quickly that it's been difficult to identify what it is. So what I did was record a video of my laptop screen during startup, on my phone. Then I was able to pause the video the moment the popup appears and I screen shot that image on my phone so I could look at it closely. It was a dialog box asking if I wanted the application "mediasharingd" to accept incoming network connections. It also stated that the setting can be changed in the Firewall pane of Security & Privacy preferences. So as I don't need file sharing, screen sharing and/or media sharing I disabled that function in the Security & Privacy settings in System Preferences. Hope this helps.