Since the beginning of time, things merge. Subatomic "particles" into atoms into molecules into bigger molecules, all directed by physics. Biochemistry, is just chemistry, is just physics.
That ignores emergent features, and that it's impossible for us to describe chemistry or biology only in terms of physics. Reproduction is one of the emergent features of biology.
That doesn't sound right to me[1]. Surely physics + enough detail is biology? Maybe it's not a level of detail we actually understand with contemporary science -- hence the addition of higher level abstractions like biology which are derived "top down" rather than "bottom up" (i.e., empirically) -- but "emergent systems" != "magic".
We should distinguish the field of physics, which is a human study, from the world, which it attempts to map or model on a fundamental level. We can say biology and chemistry are made up of the fundamental stuff of the world which physics seeks to understand, but that's different from saying chemistry and biology are just the science of physics. We have different domains for a reason. How that cashes out in the world itself are metaphysical questions of ontology, emergence, reductionism, mereology and Platonism/universals. Also the status of causality and laws of nature.
But then again, philosophy is also a domain of human inquiry. The world is just whatever it is, however we think it best to describe. Problem is that our different domains of descriptions and questions don't always fit easily with one another. So to say it's all just the domain of physics is to mistake one map for the territory.
From one perspective, mathematics is the study of the methods of reasoning on abstract concepts. Theorems follow from any set of axioms that do not lead to any contradiction. In physics, one is usually only interested in results relating to the current universe we live in. In that sense, mathematics can be viewed as more general.
The commenter is likely referring to complexity from simplicity, best shown in Stephen Wolfram's Rule 30. I'll be talking about this topic, and its implications, at length in an upcoming video on https://recursion.is/youtube.
