Help with used tetsubin care

So I am new to the tea community and I’m hoping for some assistance from some veterans. I recently received a cast iron teapot (about 8 oz) as a gift. It was purchased used on eBay, but there’s something about the unknown past of the squat, hobnailed inexpensive pot that is intriguing to me. Unfortunately, with the mystery comes the unknowns about what exactly the pot is. I’ve gathered that it is a tetsubin (like I said, I’m new) and that it is most likely enameled, as most newer ones are. However, the inside still shows rust spots. How do I know for sure that it is in fact enameled? It is slightly shiny and there are small spots where the top rubs the pot where it looks as if black paint has slightly worn off. Is this the enamel?

A completely different issue: my sister that gave it to me was under the impression by the seller that in order to get rid of the rust, she needed to cover it in vegetable oil and bake it. From what I understand, this is seasoning. So, she did cover it in the oil, but she left the baking to me. After I did some research, I found conflicting answers on whether an enameled tetsubin should be baked. I decided to just use boiling water to try to remove the vegetable oil, but to no avail. Now my tea is tainted with a terrible, stale vegetable oil taste. How do I remove the oil? Should I try the baking method or would I ruin my pot?