I recently listened to a radio interview where a comedian claimed that joke writers often accidentally write the same joke because great minds think alike. Keith Richards from the Rolling Stones and the late George Harrison have also said that the same thing happens with songwriting. There are only a finite number of musical notes, so every now and again composers are going to accidently pen a melody that sounds familiar.
And so it seems the same thing rings true for speeches. Just ask Donald and Melania Trump because in less than a year POTUS and FLOTUS have been accused of plagiarizing the work of others.