I had two brothers who were there. It was definitely not an after the fact story.
Not that I’m defending the actions or Bush, but accuracy is important.
It has nothing to do with being there.
The idea that the Iraq invasion was only about Iraqi WMDs was promoted after the fact. That is a fact. Before the invasion there were a number of reasons given for doing it. So much so that Bush was criticized by the press for not focusing on a single compelling reason.
When they decided to go to the UN, they had to decide how to make the case, and for the purposes of UN buy-in they made a decision to only focus on the WMDs. That was a conscious decision, covered in the press at the time. That can only be a decision if there were other reasons too, which there were.
Since then people have acted like WMDs were the whole story, but it never was. Just because that was the focus of the UN presentation doesn't mean the other reasons went away.