Hi again, and you're most welcome. Thanks for your patience, as I was not online when you responded.
If he had a blood clot that ruptured in his brain, he would bleed from the ear. He also could have been injured earlier, and this is what caused his seizure and bleeding from the ear.
If he had eaten from the ground that was recently fertilized and/or if he had ingested poison like Strychnine, this causes severe convulsions.
"Strychnine (gopher/squirrel) poisons: This is the most potent and fast acting poison that causes severe convulsions. The seizures from strychnine poison can be so severe that the animal stops breathing."
Other poisons, including rodent poison, will cause an animal to bleed out, internally, and that could have caused the blood from the ear, too. There are just so many possibilities, it would be difficult to say for sure what happened, but all the possibilities I mentioned, are to be considered.
Also, West Nile Virus has been killing squirrels in various areas, and this causes neurological symptoms, like seizures.
If it were possible to bring this squirrel to a vet for a post mortem (necropsy), you'd be able to find out the cause of death, but since it wasn't your pet, I assume you can't do that. With an animal in the wild (not a pet), all you can do is take an educated guess, as to to what happened, and everything I mentioned are possible causes of death for this poor, furry fellow.