A first party source, means directly from the originating party. In this case, there is no statement from Iranian officials that exists. Just 2nd hand quotes. Other first party sources would be photographic evidence, videos... like what we have of Zionist crimes in Gaza, the West Bank, Iran, Lebanon...
Iran is inhabited by indigenous people. Israel is ruled by colonizers. That is the difference. Another huge difference that impacts me as a US citizen is that Iran has zero influence on my government and there are zero laws removing my rights in favor of Iran, which is the exact opposite of Israel.