Most people think most of the time with an inner voice. Some people think more with imagery than an inner voice, and then there are some people who are just not capable of thinking in an inner voice at all. It's called aphantasia. They can't imagine sound well at all. Some of them also use imagery, but it's also common for them to not be able to imagine imagery either. But I'm sure your last idea also happens sometimes, people just misunderstanding what an inner voice is.