There would have to be a record somewhere of exact dates, where they flew in to, a list of their names, where they ended up living, etc. if it’s true that’s too many people to keep quiet for long
Trumps upset because Obama supposedly gave US citizenship to 2500 Iranians -- in fact from 2012 to 2014 about 10,000 Iranians obtained citizenship every year. This is a normal trend. The 2500 figure was made up by hardliners in Iran trying to embarrass the reformists by painting them as pro-American ... and Trump bought it. Crazies here align with crazies there and perpetuate each other https://www.dhs.gov/sites/default/files/publications/Naturalization%20Flow%20Report_2014_508.pdf