Thats just someone flicking in between fighting styles and hoping me thinks.
I even I used to do that when MKDA first came out hoping to pull one off.

It's the same thing in MKDA - if you're in your weapon stance when winning the match, and switch styles, you'll be in the 'fatality' stance holding your weapon. In any event, this doesn't say much, as you can perform fatalities regardless of which style you're in. The 'fatality' stance was a completely pointless addition in MKDA, and I doubt it'll have more importance or usefulness in MKD.

In MK: Tournament, I thought the weapon fatalities were stupid as fuck. Just in case anyone noticed, most of the time, when you slash someone with a blade, they bleed regardless. So weapon fatalities are like saying that the weapon wasn't sharp or something. They suck.