I think I figured out why all of my old photos taken with an Apple Quick Take 200 are appearing in the selfies folder. It appears to be the image resolution of 640 x 480 and camera name. As an experiment, I exported one original and then deleted it in Photos. I opened it in Pixelmator and changed the canvas size to 642 x 482, creating a one pixel white border and then saved it as a jpeg. When I imported it back into Photos, it was not put in the selfies folder, but still retained the EXIF information about the date, new image resolution and the camera name Apple QT-200. My guess is that the name of the camera needs to have Apple in it and the resolution has to be one that was used on the front facing camera of an iPhone. For example, iPhone 4 had a 640 x 480 resolution front facing camera.
Out of approximately 10,000 photos I have only two actual selfies and they are 960 x 1280 and were taken with an iPhone 6 which comes up as Apple iPhone 6, with a second line saying they were taken with the front facing camera. I also found an image taken with the the back facing camera on an iPhone 5 that was reduced in size to 640 x 480 before being imported in to Photos. It is not a selfie and was not taken with the front facing camera, but appears automatically in the selfies folder, probably due to the resolution and the word Apple in the camera name.
I now have the option of exporting all of my QT-200 photos, creating a one pixel border around each of them and importing them back into Photos to keep them out of the selfies folder while still retaining the date and camera name in the EXIF info. Hope this sheds some light on the issue.