All I can say is that if I got hit with a fire extinguisher, I think it would leave a mark.
People might come up to me and say, “What happened to you?? Man, it looks like you got hit with a fire extinguisher!!”
But if the guy went home and shrugged and said, “I got maced”, then it makes me think he didn’t get hit with a fire extinguisher.
Now you're getting the idea.
After the fire extinguisher idea grabbed and dug into the public consciousness, there was a slight correction, saying it may have been caused by a "chemical reaction," which, namely would be the mace. Then nothing. The autopsy would show head trauma, and be able to relate that to an aneurysm. But, no tape of the incident, no suspect, no autopsy. Just blood liable of Trump supporters.