This does look curiously saucer shaped, but then compare it to the second photo from the story, in particular look first at the width of the trail near the tip
First of course this photo looks exactly like hundreds of photos of a jet contrail lit by the sun, however the fact that the trail comes to a point here but not in the first photo indicates that the camera moved during the exposure, spreading the trail sideways. This is not particularly apparent with a contrail as they tend to be blurry-looking objects anyway. But with the plane, the reflection of the sun off bright parts of it creates highlights, and the motion of those highlights has created the shape of the "saucer".
Here's a good example of a contrail and a plane with a sunlight reflection, by @A380
And here's a very simple simulation of motion blur showing how the highlights can make a shape. This is just me taking a photo of the above photo on my laptop from across the room with a slight jostle of the camera as I press the shutter button
Here's another shot, much more obviously motion blur, just to demonstrate how different camera motions can create different shapes.
Motion blur is a common source of odd shapes in photos - most commonly from a small light in a dark scene. The thing to look for is the same shape repeated in the scene. Here's another shot where a small light behind the laptop is also motion blurred.
You can also see the shape repeated here in the streaks of the contrail. This also shows up in the UFO photo. Look at the shape of the "UFO" streak (like a long comma on its side) and then compare that to the streaks in the trail.