I would take this with a grain of salt. Not saying you're wrong, but it doesn't' make sense that Apple would create TWO versions of diskutil, and somehow only install that on a new 2012 mac..
Besides, the DIY Fusion drive was pretty thoroughly tested by Ars, and they didn't report this.
Again, I'm not trying to be combative, but it strikes me that the Apple tech at work may have given you a garbled explanation of what he was doing. IT at large companies think most users don't know anything, and say any old thing to fob them off.. I've had this happen