Comment: The 33,000 number cited in the original letter to the editor is the number of gun-related deaths per year. So it's actually quite accurate to include all firearm deaths, regardless of the attribution.  The point is not the circumstances surrounding each death, the point is the means of death, which is consistent: gun shot wound(s).
What's really disingenuous is to cite CDC statistics. Congress, at the behest of the NRA, has blocked the CDC from doing research on gun violence for years. 
Any parsing of gun related deaths is just an attempt to obscure the fact that guns kill tens of thousands of Americans per year, full stop.