This investment has never been secret. Google (now under parent company Alphabet) invested roughly $900 million as the majority of a ~$1 billion funding round alongside Fidelity Investments. This gave Google an initial equity stake of about 7–7.5% in SpaceX at a valuation of roughly $10–12 billion.
No one made any claim that it was a secret. The linked article is literally about public disclosures from Google themselves.
make (secret or new information) known.