Christopher concludes a journal article he has written with this sentence: "this irony points out that hunger is probably not a problem of production; it is a problem of distribution." what irony is christopher likely referring to?

Christopher is likely referring to the irony that there are a lot of countries where a lot of food production is present but along wit that there is a widespread hunger.
It is obvious that if the distribution is right the production is enough to feed everyone but the fact that there is more hunger points to other fact that here is a problem with distribution of the food. 

Mining manufacturing