Your explanation is slightly ambiguous. You say the coffee grounds are '...not used, fresh from the pot'. It can't be both, so which is it?
In American English pot has a lot of meanings. I took it as the tin where it comes, or the one where you store it at home. If you buy grinded coffee in paper packets or paper bags, you should never let it there for too long coz it loses its aroma.
How do you get it to burn?
It appears that he used a charcoal briquette to burn it.
Thank you. But how is that in the center going to burn all coffee grounds around it?