It's not about what APIs are being used to render whatever. At that level of analysis, all that anybody is every doing, is just doing memcpy and bitblt. Rather, datashader provides a framework for applying semantically meaningful, mathematical transformations on datasets as they're being accumulated, as those accumulations are converted into aesthetic/geom primitives, and as those primitives are rendered into colors. It really is "renderman for data", along with arbitrary vertex/texture shaders, driven by a dynamic rasterizer that can use whatever bins in data-space (not merely physical pixels).
BTW "Out of core" does NOT come from raytracing; in fact its history in computing is a term for anything that exceeds physical memory. We use it all the time in scientific/HPC and data science because datasets are frequently much larger than available memory.