…I don’t know, it depends on the state, but most likely they took additional coursework, got a master’s, or took enough coursework in undergrad to get certified in that area. Business education is a certifiable area in some states, so that might be how that happened. My physics and calculus teacher in high school was a mechanical engineering major in college, but he had a master’s degree in math education that allowed him to get licensed. I don’t know how someone could major in sociology and still teach - maybe they got an M.Ed in social studies education.
Information about teaching credentials in CA is available on the web: [url=http://www.ctc.ca.gov/credentials/CREDS/secondary-teaching.html]here[/url] for single subject teaching (usually in the middle and high school grade levels) and [url=http://www.ctc.ca.gov/credentials/CREDS/elementary.html]here[/url] for elementary teaching. The guide has a list of what subjects you can get a single subject teaching credential in.
Both types of credentials require that you complete a teaching licensure eligible program order to get the credential, either in CA or through reciprocity somewhere else. That program is going to be in the subject you want to teach or in elementary education. There’s also special education.
Surely, if you want to teach, you have thought about what subject(s) you might like to teach? Thus it would be most prudent if you would select one of those areas as your major.
No, it’s because linguistics and anthropology have some overlap. Since anthropology is the study of humans, and language is a huge part of the human experience, there’s understandably some need for anthropologists to understand some basic linguistics to do their work and some need for linguistics scholars to understand basic anthropology to do their work (just like I, a social psychologist, know a little basic biology to understand how the brain and hormone systems work).
Sociolinguistics and linguistic anthropology are the two fields in which linguistics and anthropology meet the most. Very broadly speaking, sociolinguistics is the study of how social life affects language, and linguistic anthropology is the study of how language affects social life. But the linguist in the room knows way more than I do and can answer this more fully!