I imagine that the Bay area is more than usually filled with aggressively ambitious people, projecting "fake it till you make it" success to both themselves and others. If everyone around you does the same, anything less than "perfect" makes you a loser, which conflicts with the self image you are cultivating. Therefore, everything must be as amazing as possible just to keep up with the rest. A sort of real life instagram syndrome if you will.

NZ (and other parts of the world as well, like the Nordic countries) have a similar reinforcing loop but in reverse. Excess boasting is seen as offensive, so nobody does it, so the average behavior trends towards modesty, making boasting stand out even more.

Yep, in NZ everyone would assume you were being sarcastic.