This so called pingpong style method can create a loop out of any source material, but the result will most likely look unnatural since you're reusing frames and it only works quite convincingly for pendular motions. The method described here finds naturally appearing loop candidates in any video stream and is way more flexible.
You may also notice that many of these looping gifs are done in much simpler way by just playing part of a video and then playing it in reverse.