Rhyming Words

Last evening I was with my son reading a book on phonics. It did have a few activities in it. He loves such activity books and he took the lead in reading and answering them. He is in UKG now and assuming that he knew what rhyming words meant, i read out a question in the book that said:
Pictures of objects are given. Spell the words and tick Yes if they are rhyming and No if they are not.
There was a picture of a Hen and a Pen. He said them correctly and continued to say:
He: Amma, Hen sings in the mornings but Pen does not sing. So what should i do???
Only then the tubelight in me realised that he took rhyming to mean that which sings. Just then Tiny walks in laughing her heart out
Tiny: Dumbo ....You don't know rhyming words??? Why are you going to school???
Me: Jaws dropped...