Of course there is more to this story. I suspect the reason there is so much confusion surrounding this attack is because it was an intelligence operation. The question is, whose intelligence was used and for what purpose?
The attack serves the interests of the central government in Baghdad by undermining Kurdish authority. Undermining Kurdish authority also serves Turkish interests--and there is a Turkish military outpost in the center of Hewler.
As for students being on the roof with RPGs and machine guns, I think it's highly unlikely and the accusation is a piece of Turkish or Arab propaganda. For one thing, this behavior is not consistent with Kurdish behavior. There have been no attacks against Americans in Iraqi-occupied Kurdistan, especially attacks by Kurds against Americans. Secondly, anyone with weapons will be under the watchful eye of the KDP. Arabs themselves cannot enter Kurdistan without submitting to numerous checkpoints and security checks, of vehicles and bodies. Thirdly, the KDP totally controls Hewler. It is not in the interests of the KDP to attack Americans. Neither is it in their interests to allow anyone to go around freely with these kinds of weapons because such would be a threat to their own authority. This is something they will not tolerate.
More information, with links to photos of the results of the attack, can be found here (from Peyamner via KurdishMedia.com):
http://www.kurdmedia.com/news.asp?id=6029
"Undermining Kurdish authority also serves Turkish interests--and there is a Turkish military outpost in the center of Hewler."
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I was wondering about the Turkish angle...you have answered it. It would not be the first time that Turkish deception resulted in tragedy.