To be fair, there's a proverb in Japan: "The nail that sticks up gets hammered down". Basically, conformity is valued in Japan, so of course the MC is going to go with "I didn't do anything special", because he doesn't want to be hammered down.
More correctly, [出る釘は打たれる], romanized as, "deru kugi wa utareru", carries the connotation that if you stand out too much people will hate you and you will suffer the consequences of that hatred. It doesn't mean "conform, or else", but rather to be aware of the risks of standing out and if you wish to avoid them, then don't stand out too much. Here it's more related to the Japanese concept of humility, [謙虚] "Kenkyo", which focuses on preventing arrogance from being too prideful (though it still links into that concept of, "don't stand out too much", too, as being prideful usually leads to rejection from a given community; this is shown best with the concept of [村八分] "mura-hachibu", which originated in rural villages and was shunning due to breaking the eight precepts that allowed villages to survive and even thrive, where everyone supported each other when in need, and was supported in turn in their need).
