The real mystery thus remains life itself. The fact that on Earth it used amino acids to express itself doesn't mean that it is necessarily limited to that single choice. It also doesn't mean that the same process would repeat in a different world, even if all the preconditions were met, i.e. the necessary for the presence of life as we can recognize it.
For all our understanding of (earthly) biology, and the tools at our disposal that we use to decide that something is alive, we still don't really know what life is, or how it begins. On another world it might as well kickstart the magic with a different medium than amino acids (e.g. more crystalline structures, some energy forms such as light or electricity, etc), with entirely different rules of replication and sustenance. It would probably make life look different to us, potentially not recognizable or even detectable.
Heck, it could happen right here, under our nose and we'd be none the wiser.