I think you make a very good point. Murrkans are very outgoing and open to meeting new people, strike up conversations, etc.
I am not sure that I would call that being gregarious though, which to me is the propensity to actually spend time with other people in public places. For example, go to most random small cities and villages all over Greece, Colombia or Morocco, and as of a certain point in the evening you will see a significant percentage of the population outside in cafés/bars/sitting in parks just chilling.
You don‘t see that in Murrka where people go home after work. Public places by definition are not a part of Murrkan social fabric the way it is in many other countries, where the culture is, by contrast, gregarious.