From reading the linked question and the answers to that question as well as the discussion in the comments there a picture of what created this artifact is fairly clear. It's not lens flare. The first answer to this question is correct when it states the following, but it also doesn't explain what is almost certainly the cause of the artifact.

These types of flares are not common in reflective telescopes.

Shooting a picture of the Earth from the L1 point between Earth and the Sun isn't common either.

• From such a position the sun is always perfectly behind the camera when the camera is pointed at the Earth.
• If the camera is pointed at the earth perfectly centered in the FOV, and if the point of the Earth's surface is level, then the surface at the point in the center of the image is perfectly perpendicular to the optical axis of the lens.
• Since the optical axis in this case is 932,000 miles long, it also means any light reflected from the center of the FoV that reaches the camera is HIGHLY collimated. Even more collimated than most advanced lasers.
• If the surface of the Earth at the center point is both level and highly reflective (such as the area in question in the example image that has a high amount of quartz on the surface), it will reflect a tremendous amount of the light energy from the sun falling on such a spot directly back at the camera.
• Since the light from the spot in question will be many orders of magnitude brighter than the light reflected from the rest of the Earth, if the camera is set to expose most of the Earth properly, the bright reflection in the center of the FoV will be fully saturated and totally blown out with plenty of light energy to spare.
• As indicated in the question linked above, the artifact is the size of one pixel at the exact center of the image.

It should be fairly obvious the artifact is the result of extreme overexposure of that single pixel and the way the image processing software dealt with the signal from that single pixel.

If you've ever observed an "Iridium Flare" in a bright daylight sky, you'll understand just how bright sunlight reflected from a smooth, flat, highly reflective surface can be, even compared to the sunlight reflecting off everything else in one's field of view.