Hi S.,
This is just a suggestion, but I personally think it's a little 'odd' that parents make a big deal out of their kids' poos when they are potty-training (I know, your boy is already potty trained). I never make a deal out of my boy's poos (2 yo potty training right now).
You 'could' be creating a monster by flipping out over a turd (lol). Think about it: is this normal behavior for adults? When's the last time you were in a public restroom and heard a woman holler, "WOO HOO, I POOOOOPED!"
Pooping in the potty is an 'expectation' for humans. Try treating it like one, and he'll (hopefully) quit freaking out about your bizarre celebrations - haha.
t