The 20-year-old threw a new world record in the class of 43.27m with his fifth effort of the competition, and marked it with a triple cartwheel before falling to his knees.
The celebration was greeted with cheers from the crowd, but the gold medal went to a Chinese athlete.
With his final throw of the competition, Wang Zhiming launched the javelin out to 47.95m to take the title.
Wang, already the Shot Put champion, said: 'It's so exciting. I used to dream about that, but I didn't think this would become true.'
Naas' team-mate Wildan Nukhailawi took bronze in a final which saw nine throws go further than the world record mark coming into the competition of 40.74m.
It was a good morning for the Chinese javelin throwers, with Fu Yanlong winning gold in the F42 class.
Fu threw a world record 52.79m to beat silver medallist Kamran Shokrisalari of Iran, with Norway's Runar Steinstad getting the bronze.
It took China's gold medal haul at the Olympic Stadium to 25.
Ukraine's Oksana Zubkovska won the Long Jump - F11/12 title with a world record 6.60m, with China's Jia Juntingxian getting silver and Anna Kaniuk of Belarus bronze.
Great Britain's Josie Pearson set three new world records on her way to victory in the Discus Throw - F51/52/53 with a throw of 6.58m.
Ireland's Catherine O'Neill took silver and the USA's Zena Cole bronze.