Secularism as I understand it does not take a position on matters theological. You live your life according to the world around you. It’s like saying Agnostocism is a religion.
But ‘you live your life according to the world around you’ is a theological position: it denies any effective existence to a transcendent realm, whether God, the gods, or the atheistic transcendence of Buddhism or Taoism. It assumes either that morality can be obtained by reasoning from ‘is’ to ‘ought’, or that morality arises solely from common consent of human beings, or is merely subjective.
As I said, it takes a position on ultimate realties, and derives prescriptions for behavior from that position, thus having the elements common to all religions.