Grad school admission after bad grade in research class for different discipline
Welcome! The gap year is a good idea. A lot of research in graduate school (and beyond) is (in my experience) similar to that linguistics class: confusing, unstructured, little guidance, figuring methods and new things out on your own, shaping your own experience. So the best way to set yourself up for success is to figure out what you could do differently in a similar situation to succeed. Where else could you find resources? How could you figure out direct questions your professor could answer? (Or that a different professor could answer for you?)

There are similar questions about recovering from a bad grade, such as this one: How does the admissions process work for Ph.D. programs in the US, particularly for weak or borderline students? and this one: Does a bad grade in one course (with otherwise OK record) affect graduate admissions?  

You may or may not need to explain what went wrong in that linguistics class as part of the graduate admissions process. But you should get it straight in your mind so that you have clearly learned from it, and so that you can deal with this better when you encounter similar situations in the future. That is, you can take charge of this story and it becomes less about that professor and more about a mistake or a problem that you've learned from and figured out how to overcome.  Good luck!