It's not clear in your description (and it's none of my business anyway) if your brother's condition actually improved (after the first two shots) or if the out-of-state flight surgeon approved him because he didn't think this should ground him.
In any event, if he had a swelling and enlargement of the heart I would think that not only would that mean he would require a medical waiver to fly, but that it would mean he couldn't take another shot on top of the two he took.
My little brother the longtime airline captain got the first two Pfizer shots. At his next FAA flight physical, a few weeks later he was grounded because his heart was found to be swollen and inflamed. He went to several specialists, they took a lot of images, and all told him he probably would not be allowed to fly again.
The airline was canceling hundreds of flights because of a shortage of pilots. They fired a bunch for not getting the “vaccines” and some like my brother were grounded with problems likely related to the “vaccines”.
Someone from the airline called my brother after he had been off for a couple of months and told him to go to a flight surgeon in a different state and that guy wrote him a waiver. There had been no change in his condition. He was having no symptoms other than a slower than normal heart rate.
After being back in the cockpit again for a couple weeks, he was told that he needed to get the booster, or he would no longer be considered to be vaccinated and would be fired.
He got the booster and within a couple days he started having chest pains and difficulty breathing. He had to go to the emergency room. His now very well documented condition had taken an unexpected and surprising turn for the worse. Fortunately, it didn't happen while he was flying.
Is that precise enough for you, or have I left out some important detail that you need to get a clearer picture?
My bet was that expedience and necessity got him an all clear to fly, and bogus at that, and his condition worsened after the required toxin injection.