It is a fact. Gold like many of the high atomic number elements is made during supernova events that occur at the end stage of the life cycle of massive stars, that is, stars more than about 5-10 times the mass of the Sun.

In fact, other than Hydrogen and Helium which were made during the Big Bang, essentially all other elements are made either in the interior of massive stars, OR during the explosions that take place when a star goes supernova.

Scientists are very careful about what they call fact. (Or at least they should be very careful!) If you come up with any new idea about how the world works, you can call it a theory. Then it might be proven or disproven or neither.

If a theory is not true, it's often easy to disprove. On the other hand, proving a good theory is usually much harder to do. No matter how much evidence you have, it's hard to guarantee that we won't someday find one piece of evidence that disproves the theory.

Remember that gravity is a theory. It's a very good theory, so good that it basically qualifies as a fact.

Elements heavier than iron, including gold, are created in the intense gravity-driven nuclear reactions that also drive the explosion of a supernova. There are other ways that these elements can be made, but have found no mechanism that produces these elements in the quantities that supernovae do.