Karika 70

एतत् पवित्रमग्र्यं मुनिरासुरयेऽनुकम्पया प्रददौ। आसुरिरपि पञ्चशिखाय तेन च बहुधाकृतं तन्त्रम् ॥७०॥

This sacred and highest knowledge was imparted by the sage to Asuri out of compassion. Asuri taught this to Panchashikha. From him this tactical system was propagated widely.

The sage indicated here is Kapila. The word 'tantra' is used instead of 'shastra' to describe the stated knowledge. This indicates it is a tactical approach to obtain knowledge that employs a trick, unlike straight forward scriptures. This is the reason why God is dealt here indirectly, and not explicitly. It does not mean it is an atheistic philosophy!