While the events play out more or less the same from manga to anime, the anime has put a much stronger emphasis on the purification that occurs directly after Nanoka hugs the boy to keep him still.

The glowing light that appears is yellow - Nanoka's signature colour, and the traditional colour used to represent Earth in Onmyoudo as well (metal being white, water black, wood green, and fire red.)

Given that Nanoka is of the earth element, and that the earthen medicine that's gone awry here was partly the work of her future mentor Natsuno, I think the anime has used this moment to foreshadow Nanoka's future role as a force of healing - a medicine that cures curses rather than a poison to feed them.

Basically, I think it was actually Nanoka's energy that caused the miasma to subside and allow the boy's leg to heal properly. Maybe this was also the case in the manga (it can certainly look that way in retrospect, but knowing how Takahashi writes...) but the anime has definitely put more focus on it as a nod to later events.