I can see a slight second internal rim at bottom, but I think he is confused with a famous $1/10 mule coin from 2000 which is very rare.
Your coin is a common mint double striking error, interesting but no real value.
Loving Halfcrowns. British and Commonwealth coins 1750 - 1950 and anything Kiwi.
If it's round, shiny and silvery I will love it.