It could have been— I think the learning is what everyone said, above and also that it triggered cravings. That could take you down a scary path...

I do a similar treat about once a month and I consider it on-plan but there are 3 differences:
1. My ingredients are 1/2 cup of liquid whipping cream (prob pretty close to the 6 tablespoons I guess), 3 tsp cocoa powder... but I use 1/2 of 1 packet of Splenda (after two years low carb, that is sweet enough)
2. I’m on a later stage of Atkins and I’ve got pretty good evidence that dairy doesn’t stall me or trigger cravings
3. That small amount of AS doesn’t trigger cravings for me

So yes, I think this could be an on-plan treat once you know how your body reacts.