People are complaining about Motti not knowing Jedi were real. But how many times did we see things written down, much less recorded video/holograms?
In this essay on how recorded media was made illegal by the Empire to clamp down on shared knowledge and control the public, I will prove without a doubt...
He would have been in the military during the Clone Wars. They served as Generals in the Republic armies. If he had not witnessed the exploits of the Jedi first hand, he most likely would have seen and heard the reports.