When I was reading Prince William's biography, I remember the author making it quite clear that he is not like a puppet. He is much stronger than what he appears to be. When he was in Eton, he used to visit his grandmother for weekends and he purportedly helped the Queen “doing the boxes.” The Queen has been training him since 1999 as to how to check, approve, or disapprove state papers, speeches etc. “Never be afraid to voice your concerns privately to your ministers,” had been the Queen’s advice to her son in early 1970s and to her grandson in late 1990s.
Considering his education and training, I would not be surprised if he also had his own input in the speeches he made and if there was something that he didn’t wanted to say, I am sure, he would’ve made it clear to the government.