Not to nitpick, but a homicide, by definition, may or may not be a criminal act. So to say that "a homicide, which is what was committed by the guy defending himself, is a felony" is a bit inaccurate, I believe.
IMHO, states should apply some common sense here. After all, arson is a felony, yet a GJ is not required to review all house fires, even though each and every one is a potential felony, absent exculpatory evidence. I believe that all "potential" felonies should be investigated and if there is sufficient evidence that an actual felony may have occurred, then by all means, convene a GJ. But convening a GJ every time there is an occurrence that could possibly have resulted from a felony act is not only a waste of time and money, but is also an unreasonable burden on the citizens of a state.
After all, executing a convicted felon fits the definition of "homicide" and could theoretically be a felony, if the execution wasn't actually authorized. But I highly doubt that Alabama, or any other state, convenes a GJ every time it carries out an execution (and lets not give the libs any ideas there).