It's probably based off the 'challenge rating' calculations for monsters/NPCs, which is explained as 'a party of four adventurers of X level should be able to defeat a monster of X CR without dying'. Intended or not, it's certainly the impression I got. ¯\_(ツ)_/¯
I've never been in a group that ran prefab adventures, though, so idk if that makes a different impression on a player. It might be fair to say 5e is balanced around a 4-person minimum party...
Experienced lurker. Generally don't say much. In the venn diagram of BG fans, DOS fans, and 5e fans, I hit all three but lean 5e.
