Why was Navdeep's silver medal upgraded to gold at Paralympics?

Javelin thrower Navdeep's silver at Paris Paralympics was upgraded to gold after Iran's Sadegh Beit Sayah was disqualified. Sayah unfurled flag that he claimed was that of Umm al-Banin, wife of Ali ibn Abi Talib, the first Shia Imam. Already having earned a yellow card during competition for a technical offence, Sayah was disqualified for unfurling the flag (second offence).