Wow, it really is!
Indeed, the image appears gray due to the fact that the background around has gray shades that merge with the overall landscape. This happens quite often if some shade prevails in the photo or picture. This is called an optical illusion, when it seems to you that an object has one color, but in fact there is a real palette of colors. Some graphic artists specifically make it so that it seems to a person that the image is of one shade. You can see a lot of such pictures here aperfectspace.com . There’s even a scientific term for this effect, but I can’t remember what it’s called in any way. In any case, it’s quite interesting.