if you don't understand how expenses should work and what a reasonable expense is then you're not a culture fit for a company that relies on employees having common sense.
I certainly know that "reasonable expense" is a cultural issue, and strongly related to family wealth.
Someone coming from a working-class single parent family making $40K/year has a different idea of what "reasonable" means than someone from a professional class family with two working parents making $350K/year.
Just because these two employees now make the same money working the same job position for the same company doesn't mean they both automatically have the same idea of what's "reasonable."
For example, is it reasonable to get room service while at a hotel on company business? As someone from a $40K/year family, I never considered it until my boss mentioned it.
So yes, it's a cultural mismatch. But the conclusion shouldn't be that I wasn't a cultural fit (because I came from a working class culture), nor that I didn't have common sense, but rather that a company's specific corporate culture needs to be learned, and explicit communications may help.