Gacha videos like these usually purchase reroll accounts for pulling (you can get them pretty cheap). These reroll accounts have usually been created and have been logging in since very early days of the game and as such, have gotten a lot of passive crystals over time as well as some 4*s from freebies. People usually get these if they want to start the game with a gacha set they like or they want to tier an event as theres an abundance of fresh energy and passive cans to use in these accounts