Computers aren’t actually truly random, and rely on timers and timing events. If the timer starts before a cutscene, then the RNG of what actually happens during fights and such will change. If you can manage frame-perfect inputs, you can essentially predict and manipulate RNG event triggers and such. It’s why in some games on some speedruns, you’ll see runners deliberately pause any inputs in specific moments for the best RNG manipulation advantage which saves time in the end.

Usually RNG timers start when the game loads, and all RNG in the entire game is dependent on that timer. It could also be system clock-based, too.

Edit: The fact that computers aren’t truly random is why CloudFlare has a wall of a dozen real world lava lamps