After all, chocolate is rather poisonous to dogs. This could have been someone's leftovers, no attempt to poison anyone need have been intended.
For instance baking chocolate has a huge 450 mg of theobromine per ounce - if the cupcakes were home-made, they are like dog-landmines.
The toxic dose of baking chocolate is 0.1 ounce per pound body weight.
This means that two one-ounce squares of 'baking chocolate' is toxic to a 20-pound dog; one ounce for a 10-pound dog.
Ok, I bothered to read the article :0)
The cupcakes had cannabis and antifreeze as well.