Pineapple and pork as a combination supposedly goes right back to the 15th century Spanish explorers and the initial colonisation of South America, when they brought pigs/pork with them to new parts of the world. Only to discover that the meat couldnt handle the temperatures, and a way to stop it going off was to use the acidity of the pineapple to extend its use days.
Putting it on a pizza is attributed to a Canadian in 1962, and remains one of the most unpopular combinations according to various surveys. something like over 80% of those that don't like it on pizza, claim they like the fruit.