For some strange and self acknowledged reason feel that the main target of the coins being hid is the source itself:

Then King Heraclius, seeing the glorious event—namely, the restoration of the holy places, which had been rebuilt by the blessed Modestus, was much rejoiced and ordered him to be consecrated patriarch over Jerusalem.


if Modestus was the re-builder of such important religious sites, he may very well be the harbinger of such treasures after the restorations, or during an attempt to flee before the over taking of Heraclius's soldiers.