Yeah, so… it's the dude's name—pretty logical move for the Biblical title-namers.
So, the book is named after Daniel, but unlike with Isaiah and Ezekiel it isn't just a compendium of his prophecies and visions. Daniel's more of a visionary than a really prophetic prophet (like, a real prophet's prophet), anyway. It isn't just stuff Daniel said, it's also tales of things that happened to him and the people associated with him. Yup, this is really a pretty straightforward way of titling a book.