If the vet is confident that Drake will be okay, then all should be well. (After he gets it out of his system, at least!)

Don't feel bad about the chocolate! You took the precaution of putting it in a sealed jar, and Drake found a way! We can't predict what are dogs are going to get into. You could put the food in a high cupboard, and he still could have found a way - anything's possiblie! Look at Angel's Maddie, who escaped her pen a few weeks ago and ran rampant through the house, chewing on the toaster and turning the stove on! 20/20 hindsight, they say... you just can't prevent every calamity!