In Jain dharma, agnikāya are fire-bodied jīvas. They are not explained by modern ideas of heat, fusion, or “reaction.” Their existence depends on where there is fire as a living manifestation, not simply on how hot something is.

So the main point is:

• Agnikāya are not said to exist only on Earth.
• They are associated with fire wherever fire exists in the world-system.
• Stars are not classified as agnikāya in Jain cosmology.
• Sun, moon, and other heavenly bodies are treated differently in Jain doctrine, not as ordinary fire-bodied beings.

So the answer is: the similarity of physical reaction does not decide the existence of jīva-types in Jainism. Agnikāya exist according to Jain cosmological classification, not according to modern astronomy.

If you want, I can also explain the five kinds of sthāvara jīvas in simple Jain terms.