It's not "Star of David", it's Star of Creation, as on one of papal tiaras
Many works on Christian iconography say that the six-pointed star is the Creator's Star or Star of Creation. Its six points stand for the six days of creation…The star also appears in decoration in St. Peter's basilica and in many Gothic churches.
- Pope Benedict XVI
It so happens that during the Middle Ages, the 'Star of David' was frequently found on churches (such as Saint Peter's Basilica in Rome) and even in mosques, but was absent in synagogues. It was also conspicuously absent as a symbol in Jewish books and on ritual objects.
- Star of David or Star of Goloka?, Fourwinds10.com