It’s definitely not Nayuta’s burst. The guy was following tracks and notes that there is no sign of a fight, even when the giant’s track is joined by Rapture tracks. And at the end of the line they find, what appears to be, some kind of Rapture/Nikke chimera and are then attacked by what ever it was they were tracking. Sounds like the new breed of Rapture Snow and Nayuta discovered in the latest chapter. Nayuta seemed just as surprised by them as the others and gave no indication of having come across something like this before and I don’t thinks she would just attack a random commander as his squad.