Mathematical chaos/order is a different category from human chaos/order.
Mathematically, the random energy of the sun is chaos and the stasis of heat death is order. Life is somewhere between the extremes.
That's... maybe not the best understanding of the concepts involved.
For one thing, the authors of D&D (and Moorcock, for the Elric stories) weren't mathematicians. They weren't using the terms in human senses, not mathematical ones.
Moreover, order and chaos are not mathematical concepts - they are
physical concepts, in that they mean absolutely nothing except when applied to physical systems.
Then, we get to a real concepts - in a physical sense, chaos is not the opposite of order. Disorder (or most properly
entropy is the opposite of order).
In this view, "heat death" is a highly
disordered state - the bits are spread all around randomly, and what thermal energy there is in the system isn't available to do work. The Sun, meanwhile, is a pretty ordered state - the atoms of gases are all clumped in the middle of the solar system, and a whole lot of energy in the system is available to do work.
Now "chaos" is a matter of how
predictable a system is. While order and disorder can be measured of an instant, chaos is a matter of
change over time. WIll that ordered system change predictably over time? Then it is not chaotic. If its change over time is not predictable, then it is chaotic.
Chaos is also an issue of
scale. On the microscopic scale, a drop of water from a pond can seem chaotic, with lots of microscopic life moving around in unpredictable ways. If you pull back, and look at that drop from far away, that drop doesn't really significantly change over time. It just sits there and slowly evaporates.
This is relevant when we think about the Sun - the detailed movements of plasma in the outer atmosphere is not very predictable. The large scale flows of plasma inside are more predictable. And, from outside, considering a timescale of thousands of years, the thing is even more predictable - it just sits there and shines.
But all the while it is shining, it is going from a state of relatively high order, to one of disorder.