The joke's been around for a long time, I was not very old when first time hearing sarcastically "eat your plate empty, because if you don't, some kid in Biafra will starve".
You are the only person besides my mother (born in the late 1950s in the Southern USA) that I've seen/heard mention Biafra. Her knowledge of Biafra was due to her being told a similar thing as a child, "eat everything on your plate because there are Biafrans starving."
I was less than 4 years old when the Biafra war ended, but it lived in public consciousness here longer due to a church [1] being built at the time, and some students spraying big red letters BIAFRA to the rock wall to protest church construction when people were dying of famine over there. It's an iconic photograph of 1960's here.
Not that it would have been very easy to relieve that famine with whatever amount of money, without military intervention.
Biafra received also special attention from my country because they adopted "Finlandia" by Sibelius as national anthem of their short-lived nation (with different lyrics, but same theme about rising from oppression.)
