Ishwara Pranidhana is surrender to ultimate reality. Using the other 9 yamas and niyamas in conjunction with this, we learn to be present with what is, seeing life as arising in an infinite field of Consciousness.
Please interpret this niyama in a way that feels comfortable to you. Some people see this as surrender to God. For some people, being absorbed in nature feels like worship.
Yoga philosophy is non-religious. Swami Rama encouraged students to think for themselves, to question and experiment and make the philosophy their own. Many students practice yoga meditation as a spiritual practice. Others have a variety of other approaches. All are absolutely fine.