TL/DR: it's not. And for a fake, it's a pretty bad one too. Besides all of the points the Aviation SE users noted, notice how all of the passenger windows were photoshopped out except the ones partially overlapped by the large IndiGo logo at the front of the plane, which would have required some more work...
Yeah, but I love the way user DeltaLima on Aviation SE left this detail until the very end of their answer. This would have been enough to settle the issue on its own, but of course pointing out all of the other details gets more upvotes...
Wow, I noted it looked strange and spotted some things other people mentioned, but somehow completely missed the windows... I'm sure there is some sort of name for this thing of not spotting the obvious while getting the details.
Banner blindness is more a web term, but maybe fits as the logo could count as some kind of banner/ad which we only glance over and won't pay much attention to it.
It's pretty good if it were an AI generated image fake. That was my immediate thought, and then changed when the only differences were things like 'it should read AVAF not AVAX'.
Larger image: https://i.stack.imgur.com/DQdIY.jpg