re: You tell me
If we are talking about the habit of discounting sources that disagree with your point of view, while highlighting sources that agree with you, there's a lot of that going around.
We don't know why the intelligence services discounted these two guys' statements. Maybe they had a known history of providing false information.
There are apparently a number of terrorists, some with links to Al Quaeda, who have fled to Iran from Iraq. I suppose it's possible they were in Iraq just because it's such a hot vacation spot, but one wonders.