This is a set seed speedrun, first attempt failed (caught by cobweb) so the streamer used mod to reset speedrun.
The stronghold is that close to spawn, I checked that myself with seed in description.
When ender dragon hit the player, the speed can be transfered to arrow if you time it correctly, so one shot ender dragon is possible. (expatiation video is linked in video description)
Each individual end portal frame block has a 10% chance of containing an eye of ender, as determined by the world seed. This means there is a one in 1 trillion chance for all 12 end portal frames to contain an eye of ender,
That never actually occurred to me - NGL I know how it works but never gone to end. I do also wonder how much was items placed in the exact right place, or just the absolute perfect seed.
There is a "point" in ender dragon's hitbox, when player gets close to it gives the player very high velocity, by shooting an arrow before player gets damaged and go flying, the velocity is transferred to the arrow, one shot the ender dragon.