Was this Method Accurate?

Reading chapter eight i came across many things that stood out to me. One of the main things that stood out to me was the fact of how they went about taking the 1910 census. It is crazy that they just asked people who their mother tongue was and off of that they assumed their race. It just doesn't seem like a legitimate answer or way to go about things to me because what if someone didn't know their mother tongue? Did they just not include them in the census or what? I just feel like it was not a reasonable way to conduct things and that if they were conducting a census again they should do more research on a group of people.