Charcoal isn't coal. There are several types of natural coal and charcoal, and they all have slight differences in density and chemical composition; so they probably all look a bit different when burning. Just like how different brands and types of charcoal can also look slightly different when burning (such as one kind throwing off sparks while it ignites and another that doesn't).
I've never seen natural coal burning. But I've seen at least 3 types (not just brands but actual differences in how they are made) of charcoal burn, and they all give quite a different "show" as they do.
Coal is a natural mineral that forms over the span of millions of years while charcoal is a manufactured product created from wood. While coal in its natural state is never used alone in a barbeque or smoker, it is commonly added to charcoal briquettes to increase the energy density.