If you check very old posts for Eek Parton, you can see first build of game was in Nov 2015, and game released to the early access on Steam (0.6.x) in 2017 around September.It would take a solo dev years, and a team a minimum of a year or so to put together something even remotely close to House Party.
So it took single dev almost two years to do this (prbably more, since we do not know amount of effort for first game build). But most important thing, he is programmer, not an artist. Most of early graphics was all 3D DAZ models, Unity asset store for the house, etc...
Then game got huge populatiy, team got extended and we have game what is today almost 3 years after that.