Video presets use non-square pixels which is why you're seeing the image stretched after you save it. When you create a new document using a video preset it automatically uses Pixel Aspect Ratio Correction so what you see on screen is how it would look if the pixels were square. You can turn the correction on and off under the view menu.
You can also change the pixel aspect ratio of those files, and any other files, by selecting View > Pixel Aspect Ratio and then selecting one of the aspect ratios in the list. Square Pixels is what you use for anything other than video.
Is there a reason why you're selecting one of the video presets? If you're not going to be using the images in a video file there isn't a reason to use the video presets.