Any Indonesian noun can either be plural or singular. However we can either use repeated word to emphasize that the object is plural; or a counter to emphasize that the word is singular. Example : "Sebuah apel" is an "apple". (Sebuah is a counter of one object) "Apel-apel" is "Apples".
Generally we can assume the noun is plural or singular from the context though
The way he pronounces apel is not right. It has two possible meanings depends on how you pronounce it (but same letter spelling) He said apel which means assembly, usually used in word 'Apel pagi' which means morning assembly. While the one he means is apple, it shld be pronounced with 'p(ə)l' is the same as peo'ple'. So apel.