Need advice

I did, actually. Because I just could not understand what happened.
Unfortunately, my vet could not tell me very much.

I just don't get it. I have read a lot online about it. I know pneumonia does not happen overnight and he was not coughing or having a fever. He started having some congestion on the 26th, but as he had seemed to be getting stronger to me, I thought it possibly was side effect of vaccines showing up.

I know that he initially fell ill 4 days after receiving his vaccines. Whether it was something from before he came to live with me, or I have read about a link between bordatella vaccine and pneumonia:

Bordetella and Pets

The Kennel Cough- Bordetella Vaccine Controversy

Maybe a lowered immune system from the stress of moving? We just don't know exactly. I can't help but wonder how it was not caught when he was at the vet, as he was there for full days to be monitored, but again he was asymptomatic and his tests were normal several times.

I did select cremation so that I can always remember our time together, no matter how short. His breeder is a wondering and caring woman and we were in constant contact throughout everything. She is just as heartbroken as I am.

Any thoughts? Have you ever read about a link between vaccine and pneumonia?

I really don't like that bortadella. It's a terrible disease for any pup to get, but the intranasal is a live vaccine and they do get a very mild form of it. Phoebe honked for two weeks straight after we got her from the pound and they gave an internasal. Taggert got his too, and with him, he didn't honk, but foxxy got sick from taggert's innoculation and honked for about two weeks, and she was on prednisone for a reaction to heartgard at the time. I don't board my dogs so they don't get it at all any more.

With sick puppies you can absolutely go back to goat milk or milk replacer. the 4-8 week weaning is't completely set in stone as far as a liquid vs. solid meal goes. Some pups take longer to mature. If you need to keep a liquidy, mushy diet for longer, and the pup needs more protein, whey protein might be added, or even blood meal. I don't know, I prefer blood meal or straight up blood if you can get it (like the kind you get from the butcher to make black pudding) over egg for dogs that need more protein. Egg has enzymes in it that block B vitamins. Blood has more dissolved vitamins and minerals. Dogs are carnivores, so they can easily digest blood.

and no soy. Soy is actually hard on their kidneys. But as for the aspiration pneumonia, that can happen to any pup. Likely, he aspirated because he was just barely learning how to eat his mush. That happens all the time. The second thing that happens is that the pup's stomach refluxes because there is a valve that may not be fully formed yet and they aspirate the reflux. That's also too common and completely unpreventable. It's not a failure to thrive, it was just something that happens sometimes, and we can't do anything to prevent it. A dog has to learn to eat solids. Sometimes things don't go well. Accidents happen. But sometimes looking for the answer is actually more harmful. He was very loved for his brief time. That's all that really matters.

I am so sad for what happened to your pup. being a puppy is so hard. There's so much that they have to do and develop and learn in just a few short weeks, and so much can go wrong at any time with nobody's fault at all but just plain old bad luck. It's so sad when they don't make it.

That still does not mean you should listen to a junk science anti-vaxxer opinion like the article you put up there. as much as the vaccine is a pain in the butt it still works to train your dog's immune system. Bortadella is no fun. neither is rabies, parvo, distemper, and the host of other things in that combo shot. I know you are looking for answers to what happened. "Holistic" methods that include homeopathy to solve various "miasms" and "agues" are straight up medieval. pseudoscience is not the way to get those answers.