Well, going all the way back to 1Ed for inspiration...a shapechanging dragon could appear as almost anything or anyone, like the mobile court of Bahamut and his 7 gold dragon attendants disguised as an old sliver-haired man surrounded by 7 canaries.
Here, the BDE could appear as something equally non-threatening or non-intelligent creature in the tent, while his vizier runs the show as if either HE were the emir or the emir "is unavoidably detained with other business," all the while observing the PCs in secret.