Freddie's line about Brazil ("where the nuts come from") is likely a reference to the famous British comedy play 'Charley's Aunt,' in which this is a repeated line.
In the original story on which this episode is based, the name "Popjoy" is derived from a misunderstanding of the words "Dog Joy." In the story, Freddie is trying to sell a product called Donaldson's Dog Joy (biscuits).