The NextPlatform article hints at their approach: “We have got this scheme for the mask ROM recall fabric – the hard-wired part – where we can store four bits away and do the multiply related to it – everything – with a SINGLE TRANSISTOR. So the density is basically insane. And this is not nuclear physics – it is fully digital. It is just a clever trick that we don’t want to broadcast. But once you hardwire everythin…
I stand corrected here. The design is "fully digital". They are not using analog trickery here. They are most likely just using a clever collection of very tiny transistors hooked up to two wire layers such that one _digital_ transistor can trigger the correct 4-bit output. This can be accomplished through clever logic design.