Yossipon is a medieval retelling of Josephus, from the tenth century. The author calls Josephus Joseph ben Gurion, although his father's name was Matityahu. Rashi quotes this work and he thought that it was actually written by Josephus, but in the manuscript of the book, it tells us when it was written.
Wow! So you know better than Rashi. Thank God we have someone in our generation bigger than Rashi.