photon emission - Why do atoms (iron eg) glow with all frequencies of light when exposed to enough thermal radiation?

Correct me if I'm wrong, but objects (made of constituent atoms) glow with a particular frequency of light which our eyes relate to as colour.

They glow when a particle in a higher energy quantum state gets converted into a lower one by the emission of a photon. And the energy difference between the two states will correlate to the frequency of the photon.

So when we look at an emission spectrum we look at many colours being seen from a sample, now why are there so many (more than one)? Is it because there are many energy levels and the difference between these energy levels vary? Is it because of electrons being promoted and demoted from n=2 to n=1, n=3 to n=2, n=4 to n=3? But aren't these energy states unstable also, won’t they all emit photons till they reach n=2?

Is that why iron's electromagnetic radiation is first within the infrared range and then progresses to the visible light range because the electrons are now in high enough energy levels that the frequency of the photons can be detected by our eyes?