you may have inadvertently used a feature of photos in ios called "live Photos.
"One of the new features in the iPhone 6s and 6s+ is the "Live Photos" feature, or as I like to call them, Harry Potter Pictures. To take one, you just have to enable the Live Photo option at the top of the camera, much like turning on flash or HDR options. After you do that, your photo will be a still photo, but it will include a low frame rate "video" of 1.5 seconds on either side of when you pressed the button for the photo. I have to put quotes around video because Apple says it is a Live Photo, not a video."
And from Apple. " https://www.apple.com/ios/photos/
Introducing Live Photos.
"A still photo captures an instant frozen in time. With Live Photos, you can turn those instants into unforgettable living memories. At the heart of a Live Photo is a beautiful 12‑megapixel photo. But together with that photo are the moments just before and after it was taken, captured with movement and sound.
You can bring those moments to life any time by simply pressing anywhere on the photo. You can even set your favorite Live Photo as your Lock Screen wallpaper, so you can relive a moment any time your phone leaves your pocket. And you can view Live Photos on your other Apple devices, too."