While I can't really know the circumstances surrounding your case, I wouldn't personally consider it sexist as long as it's respectful and in equal spirit to the rest of the class (regardless of gender and sex). I had a teacher in my high school who called all guys "son" and all girls either by their first or last name. She was just a firm, but polite older lady, we never really thought anything bad about it.
To summarize, I don't believe it's sexist or misogynistic as long as you receive equal treatment and fair consideration. Of course, it heavily depends on the tone, situation and the person in question, but it generally seems pretty friendly and endearing. A lot of older people are like that, at least in my experience. I've been called anything from "son" and "dear" to a "wonderful young man".