Yes,Joseph C.Wilson really did find that Iraq tried to buy Uranium in Niger.This does not necessarily mean that they had developed WMDs or even had the technology to go forward with such plans.This does not take away from fact that Iraq did try to buy Uranium in Niger but at the same time does not prove much of anything
Wilson claimed many things over his time as a diplomat, but the idea that he influenced the entire invasion of Iraq is very much over drawn. There were so many reasons that the Whitehouse decide to invade Iraq, and if this information was not the cause, others would have been.
Yes, Joseph C. Wilson really found out that Iraq tried to buy uranium in Niger, because it does not make any sense that Joseph C. Wilson was trying to start a war with information that was untrue. Wilson was liberal, and was no friend of George W. Bushes. There's no way that Wilson was war mongering. He said what he thought was true. Iraq wanted to make nuclear weapons.
In his op-ed peice "What I didn't find in Africa," Joseph C Wilson explicitly outlines that he did not find evidence of any attempt, successful or otherwise, by Iraq, to purchase or otherwise procure nuclear materials from Niger. The mines in Niger were controlled by international interests and are highly regulated through international agencies. If such an attempt had been made, something would have been left as evidence. However, all of the yellowcake that was mined, moved, stored, sold or transferred was all accounted for. If someone did intend to sell Iraq Yellowcake, it was not under any authoritative entity.
Joseph C. Wilson probably didn't find out Iraq tried to buy uranium in Niger since there were no weapons of mass destruction found in Iraq whatsoever. When Wilson spoke out against the Iraq War, his CIA wife was outed in revenge. Wilson was just doing his job and got in trouble for not finding evidence of anything.