No coincidence at all.

Remember, Scharnhoff has lived in Jerusalem for fifteen years.

He seems to have satisfied himself that the Tomb of the Kings is directly under the Dome of the Rock.

How is he to get to it?
The Dome of the Rock stands in the middle of that great courtyard, with the buildings of the Haram-es-Sheriff surrounding it on every side, and hardly a stone in the foundations weighing less than ten tons.
"He reasons it out that there must be a tunnel somewhere, leading to the tomb, if it really is under the Dome of the Rock.

I have found out that he went to work, while the Turks were still here, to find the mouth of the tunnel.