The special thing about this is that creating new rice cultivars are difficult. Indian farmers specifically discovered and developed techniques to prevent self-pollination and encourage cross-pollination. This allowed for an explosion of rice varietals.

In other words the special part here, along with the quantity, is that the process was deliberate and encouraged. There are like 110,000 identified cultivars of rice in India. There are special harvest festivals that specifically encourage the discovery of new rice varietals which are then shared in these festivals.