They are making it from scratch. There are lots of sources but this is the first one I found. I assume they package it as well.

https://www.tomshardware.com/pc-components/ddr5/chinese-memory-maker-cxmt-enters-the-mainstream-consumer-memory-with-corsair-vengeance-ddr5-kit-chinese-made-dram-emerges-as-an-antidote-for-crushing-shortages

Foxcom assembles sub models into complete products. Still higher than slave labor level skills, but not as high as chip fabrication I admit. You need a skill base to assemble phones at a high level.

I mean making the machines to make chips and making a factory that uses said machines are two different things.

There are already factories in China making DDR5 and DDR4 ram now days.

Huawei would just provide the support and resources needed to scale up a new large factory.

No slave labor needed. All you need is a modern, advanced, high skill, responsive industrial base which China has.