It was over 25 years ago, but there has always been a certain degree of paranoia among some "allies" .
I was on the sidewalk, which was/is US territory. My camera was handed back to me by the DC police, after they took it from the Saudi guards. The decision to lay on the ground was my own. I didn't understand a word the guards were saying, and I wanted to appear as compliant as possible (remember, they had guns...). After it was over one of the State Dept guys said it was a smart move. If the guards had forced me beyond the gates, I would have no longer been on US property, which may have complicated my release. Still, the whole incident began due to a Secretary failing to inform his people I was supposed to be there, and I'm sure it also would have been cleared up quickly. The Secretary was very apologetic.
As an aside, I was treated really well by other embassies. At some, I was invited in, offered food/beverages, and even met a few ambassadors.