Alright, I watched the run for this episode today, and I noticed a couple of things. First, when Tiffani is in the Chamber of the Sacred Markers, the door leading up to the King's Storeroom moves as though a temple guard is hiding behind it. Secondly, a bright light flashes when the doors open out of the Chamber, which typically happens only when the door leading up to the King's Storeroom is unlocked. And third, even after she grabs the helmet, the door doesn't open.
I suspect that the reason Tiffani got all the way to the room without encountering a temple guard on this run is a production error. My theory is that the door going up to the King's Storeroom was supposed to open in the Chamber, revealing a temple guard. Because it was stuck shut, the temple guard couldn't come out, and when she gets the helmet the door remains closed because it's stuck. (That poor trapped temple guard.)
The temple run from this episode from
http://mandarinhand.cjb.net has somehow found its way onto YouTube at
so you can watch it and let me know what you think.