Thank you for your patience. Yes - the ingestion is definitely a worry, particularly given your boy is just a young small breed dog. There are a number of potential consequences from caffeine ingestion like this in a small, young dog including anything from vomiting and diarrhea, to tremors, excessive shaking, increased thirst and respiration, hyperexcitability, seizures and potentially worse.
Hopefully Zack ate these in the last half hour or so, as you would be able to get him to vomit these up again. There are several ways to induce vomiting, however 3% hydrogen peroxide is the most effective. As it has been about half an hour - he will likely vomit this up pretty easily. You can read about how to induce vomiting in dogs online here:
If he doesn't vomit, or if he vomits, but the coffee grounds don't seem to come up, then you are best to get Zack straight down to your local ER vet where they can either induce vomiting again, or start him on some intravenous fluids, activated charcoal and monitor him over night. If he does vomit the grounds up, then do keep an eye out for any of the symptoms mentioned above. In particular, please also keep a close eye on his mucus membranes, capillary refill time and respiratory rate as follows:
Mucus membranes - flip his lip and look at the color of his gums. They should maintain a nice salmon pink color. Get him to the emergency Vet if they appear white or very pale pink, or if they are a dark deep red color.
Capillary Refill time - this measures blood perfusion and test this by putting your thumb on his gum to apply pressure. After you release your thumb you will see the gum blanch. Capillary refill time is the amount of time it takes (in seconds) for the gum to return to a healthy pink color from the blanched white color. If 2 seconds or less don't worry - if it is taking significantly more time, again - off to the emergency Vet.
Respiratory Rate - if he is continuously panting throughout the night, this is a sign of shock and or pain and a signal for a trip to the emergency Vet.
I hope all of the above makes sense? If you have more questions or if I can help in any other way, please do not hesitate to ask! If you would like to accept my answer, please press RATE OUR CONVERSATION (I am not compensated in any other way). Bonuses are always welcome. Thanks! I hope to work with you again soon!
PS: If you have additional questions after you rate the question, you are welcome to request me for additional conversations if I am on-line or by beginning your question "Dr. E..." or "Pet-doc..." and others will leave the questions for me.