How does Ehrman support his assertion that the "we" passages in Acts represent a false claim to eyewitness status for those particular events?

A Wikipedia article on the Authorship of Luke–Acts has a quote from Bart E. Ehrman commenting on the stylistic insertions of the "we" passage as indicating a forgery: > According to Bart D. Ehrman, the "we" passages are written by someone > falsely claiming to have been a travelling companion of Paul, in order > to present the untrue idea that the author had firsthand knowledge of > Paul's views and activities. Ehrman holds that The Acts of the > Apostles is thereby shown to be a forgery. The traditional view is that Luke wrote Acts and Luke traveled with Paul on some of his journeys, so the "we" passages are the parts of the journey where Luke was present. On what grounds does Ehrman push back against this view, so as to make the case that these stylistic changes prove the book is a forgery?