At one point a company I worked for had a similar setup and we did much the same thing. Our office basically turned into a small dorm room (we were all in our early 20's at the time) kind of like you see on the show Workaholics. We had posters, jokes, a whiteboard covered in notes and stupid drawings, we even had themed playlist days where we'd come up with what genre or theme of music we'd have playing... 90's day, it's a cover song day, you're embarrassed you like it day, ska all the things day, etc... It was one of my favorite times/jobs I've had because of that atmosphere, we all learned a ton and collaborated on each other projects and spent way more time at work without even thinking about it. We ended hiring more devs and moving to an open office environment and everything changed, we all were still clustered together, but collaboration slowly faded away, where we used to turn around and talk to one another we now communicated over IM even though we sat less than 10 feet away, partly because an open office means everyone is interrupted as soon as you talk, make noise, play music, etc.
I always just through it was the growing company that lead to the change, but now that you mentioned your experience and I reflect on mine, I think that little 3 man shared off might have been the key to all of the awesomeness and fond memories of my time with that company.