No, not even close. With your logic, one could easily claim that ANY equilateral triangle (upside down or not) is the mark of the beast 666 because they contain precise three 60 degree angles (60, 60,, 60 = 6, 6, 6). Besides, every single online source that has even a single shred of authority states quite clearly that the Star of David represents the number 7, not 6 (or 666). This is because the Star of David has exactly 7 parts or segments- namely the 6 external points (6 days of Creation) plus the central hexagon (1 day of rest, Sabbath day). One online Rabbi explains this quite thoroughly:
Many commentators have suggested that the message of the Star of David is linked to the number seven by way of its six points surrounding the center. The number seven, of course, is key to our understanding the world as a holy creation of God. The earth is the result of a divine plan, not an accidental Big Bang. The world represents the vision of a Creator who after completing it took the time to rest, to evaluate, and to proclaim it “very good” – fulfilling His expectations. In short, the world is holy, a place in which man and everything else created in the six days has the potential to revolve and evolve around its center, its core and its Creator.
The Sabbath, the seventh day every week, is a reminder of this concept. Every seventh year, too, is a sabbatical year in which the land is not to be worked, and after seven cycles of seven years the Jubilee year brings freedom to indentured slaves and the return of property to its original owners.
This emphasis on the number seven as a sign of the holy finds another illustration by way of the menorah in the ancient Temple. The menorah was comprised of seven oil lamps resting on three stems branching from each side of a central pole. Three on each of its sides turned towards the center, six in all directed towards the midpoint, the seventh. It has been strongly suggested that the Star of David came to be used as a standard symbol in synagogues around the world precisely because its organization into 3+3+1 – triangle up, triangle down, and center – corresponds exactly to the menorah.
– The Star of David and the Mosque, by Rabbi Benjamin Blech