Sadly this is not true at all. My dog ate dark chocolate once and I had to get his stomach pumped (a kid at a party fed it to him). And my friend's dog ate slug bait and died.Dogs can sense when some things are bad for them, I tried giving mine a little bit of onion and he wouldn't touch it (thank god cos they're poisonous!! I didn't know!) but with sweet things they won't have a clue, they'll eat anything it's not because they 'like it'
Chocolate icecream won't kill a dog (concentration is too low) but I imagine that paired with the dairy in the icecream, it won't make its tummy feel too good. I wouldn't want to be the one cleaning up the garden afterwards either, IYKWIM.
For anyone who doesn't know, the most toxic human food items for dogs (in order) are dark chocolate (60+percent, although a huge amount of milk chocolate could be fatal for a small dog), macadamia nuts, raisins and grapes, onions and avocado.