The so-called 'lyricist' of that song is none other than the legendary king of dub himself, Mr. Lee 'Scratch' Perry. Scratch could be considered, putting it mildly, as 'eccentric among eccentrics'. He's 81 now and in recent years has produced less and less coherence in his lyrical output, even by his standards.
In this song, he is largely improvising around the word do (Scratch is 'Dr. Do') by using other words that rhyme (boo,coo,foo). If you listen from 2:55, I think he says:
I no crazy, mon. (I am a king! I am a meeny meeny meeny!)
What I would do for you.
What I do, will do.
Who I boo, will boo.
Who I foo, will foo.
Who I coo, will-
I foo China. I foo Hong Kong.
I foo Mr. Wong. And I foo Mr. Kong.
I foo China.
As a lifelong fan, my intuition tells me that the I foo China lyric was completely unplanned and came to Mr. Perry suddenly in a flash of inspiration. As for what it means, only Scratch could tell you, and even then I'm not so sure.