Paraphrasing what it says
here:
"During seed propagation of an unvariegated wild collected plant from Hiroshima, [many] Fugaku appeared. Of those, a small number of them had green stem and green roots and were called Aojiku-Fugaku. Nowadays, many seedlings of these original Aojiku-Fugaku are in circulation..."
Basically, Fugaku and Aojiku-Fugaku were originally discovered together as a group of siblings.
However, since both Fugaku and Aojiku-Fugaku transmit their variegation to their offspring when selfed, most of the Fugaku and Aojiku-Fugaku currently on the market are seed grown from this original group.
However, by seed propagating normal Fugaku, there is always the chance that some of those seedlings could mutate and be unable to produce anthocyanins, and it would be acceptable to call those Aojiku-Fugaku as well.