Setting up dev env. in one day is normal, it normally shouldn’t take more than couple of hours at worst but how did they managed to publish a commit next day?

Setting up dev env. in one day is normal, it normally shouldn’t take more than couple of hours at worst but how did they managed to publish a commit next day? What type of a code base was that, because normally an engineer should spend at least couple of days trying to understand the full code base.