The singularity from the FLRW metric is interpreted to mean that current theories are inadequate to describe what actually happened at the start of the Big Bang itself. It is widely believed that a correct theory of quantum gravity may allow a more correct description of that event, but no such theory has yet been developed. After that moment, all distances throughout the universe began to increase from (perhaps) zero because the FLRW metric itself changed over time, affecting distances between all non-bound objects everywhere. For this reason, it is said that the Big Bang "happened everywhere".
