The creator has all rights to make screenshots with post-process. Same as Nirvanochka has a black background, some light, and maybe the camera was adjusted.
As you read a description says LOW POLY MODEL. Besides, that character has 51 animations, texture options… and all that for 20$.
Please don’t harm that creator girl, you can always contact the seller. I believe she will tell you quickly how to make the same image that she got on screens.
Have a nice time.