I'm also wondering....
Its easy to make different batches by diluting some to the fermenter, or by dry hopping.
Or even by mixing wort,
But I'm not sure how it happens here
Donoroto got it. But also the weight to lift. What I done is split the worth into 2 batches. 2 different yeast, 2 different hop and adjunk additions. This was from a Bohemian Pilsner. But the main point of it all was saving time! We are 2 of us and always do 4 brews at the time. This was the last brew before the Florida summer. If you stand around a pot drinking beer you are not brewing.
I've done 4 distinctly different 5 gallon batches in one brew session with a 15 gallon max boil capacity. Basic wort divied up and topped up/boosted slightly with DME additions, separately mashed/steeped specialty malts where appropriate, short boil for different hops and then different yeasts. Got a Golden Ale, Witbier, Irish Stout and Hazy Pale. Good way to fill the tap fridge.