Although content writers aren't supposed to know much about SEO but if they do it's a added bonus because writing and SEO go hand-in-hand and website popularity depends on the right balance between the two and not just one of them. Obviously if you have mentioned SEO as one of your skills then be prepared for some searching SEO questions from the interviewer. Even if you mention SEO as a separate skill as distinct from SEO content writing, mention it after your writing skill and not before that. But handle all SEO related questions with tact. If the interviewer just has some basic SEO knowledge then you can convince him/her quite easily by talking about on-page and off-page optimization but if the interviewer has in depth knowledge then you will need more than just SEO basics. So it's advisable to state upfront your comfort level with all things SEO.