Both the oi and oy vowel pairs make the same sound. So how can a student distinguish between the two?

A good rule of thumb is to use oy at the end of a word (or the end of the first part of a compound word, or the end of a word before a suffix is added) and oi if it is not at the end of the word. There are exceptions, but that general principle will work with all ten words in this fun level.