Tell us about yourself!
It seems to me that the difference is only in the material used. But the design is copied. If this is an instructable on how to make Laughing Stones by Hirotoshi Itoh using concrete, then this should be indicated in the text.
It seems to me that you tried to repeat using concrete the sculpture `I Know You` by Hirotoshi Itoh. But I think you should indicate whose work you were inspired by.