I think you missed their point. Their frugality went beyond what the company size/stage/etc necessitated, and it's because of their upbringing. I'm the OP and I can relate.

I grew up both poor and was an immigrant. My parents took up blue-collar jobs and were themselves trying to understand how things work in this country. I grew up in a community of immigrants so all my friends were in the same boat.

If you don't have anyone in your life who goes on business trips or tells you about their white-collar job and how things work, how are you supposed to know? Well, through your own experience! Which unfortunately involves doing something stupid at first and learning a lesson from it.