If you trace back the cosmological evolution of our universe you’d get a “singularity”, that is not the same thing as being a single particle. Even the physical existence of a singular point at the beginning is not accurate. A singularity in physics is a mathematical artefact signaling the breakdown of the descriptive power of the theory you are using. The common example is the singular behaviour of the electric field around a charged particle in classical electrodynamics, the singularity is a signal that you’d need to switch to quantum electrodynamics to describe the physics close to a charged particle. Similarly with cosmology: close to the beginning we have a singularity that signals the breakdown of the descriptive power of our theories, and we need to switch. What we would switch to we call a " quantum gravity theory", but we are not yet sure what that theory is.