What we thinking to this?

NeGativ4k send me this video yesterday and after watching it I do agree that it looks like Zakky might be using turbo, he doesn't miss a beat during all the boss fight and that's imo impossible to do because you have to press the other button to reallign your weapon. Can some expert have a look?

I watched the second part of your video side by side with the WR video and IMO it confirm that he used turbo... Another red flag is that he turned off comments on his video, lol.

Last boss vs turbobuttons 15.20.30 times per seconds

looks like he cheated on other "speedrun" too : https://imgur.com/a/EIpYF4K

i am look last boss fight wr holder, every frame and i said he used turbo buttons, all fight he attacked every 3 frames.

Is Item C allowed？

Allowed yes.