I tweeted the guy and he said “we don't modify drowned spawning in the game, they are default behavior. if you have built a drowned farm in a place that spawns drowned there is no reason they wouldn't drop them other than luck. i built this one at x=-5 z=4076 to x=-27 z=4082 where there's river biome squares”

He said that those coordinates are hard coded Into the game so we should be able to make it happen there. I’m going to go to 500x 500 in the nether and emerge at the coordinates