Isn't K???a a god?

Rudraksha is not a god, he is a Buddha.

In Buddhism, the gods, belonging to the ghostly beings, are blessed ghosts, whose blessings are great, but are in the nether world. Wisdom is limited.

The Buddha, on the other hand, is a being whose wisdom and blessedness have reached perfection, and is called a two-footed deity.

Also, Rudra and Buddha, are two names for the Buddha. So-and-so Buddha, may also be called so-and-so Rulai. Such as Shakyamuni Buddha, can also be called Shakyamuni Rulai. Folk say Rulai Buddha, generally means Sakyamuni Buddha.