its not. MK_Sarah confirmed it was a special move when the picture of Lex doing that attack to Kitana surfaced.

But was Kitana burned to a crisp? Let's face it, even in 3D games, regular special moves have turned into fatalities (Scorpion's Spear in MKDA, Toasty in MK4 was a special/fatality, Ermac's teleslam, the list goes on) Besides, there's no real way to tell because the screen doesn't go black for fatalities in this game

I remember when i made a thread called Lex Luthor Fatality Screen but everybody said it was a special

well perhaps thats because as you progress through the match the damage gets more visible. so probably the more times you do that attack with lex, the more burnt your opponent will be. its like what shang's sou steal move does. the more you do it the more withered and you opponent will get.