If you find yourself in the situation of the calculator-assuming woman, where you feel like you've made a comment that touches on cultural sensitivities, use the moment as a learning experience. Instead of leaving the awkward air, ask them what they are thinking. "oh sorry haha that was a weird assumption, what is it?" Asking to be educated is pretty much the opposite of the mansplaining / whitesplaining that is so painful to the author of qu33riosity, and is almost universally welcomed. A little humility goes a long way.