No reasonable person needs to wonder any such thing.

Murder is the unlawful killing of another human being. Someone who unlawfully and intentionally uses deadly physical force against another human being can reasonably be charged with "attempted murder".

The key word here is "unlawfully".

Not every intentional use of deadly force, including deliberately shooting someone, is unlawful. If it's not unlawful, it's not "attempted murder".

In this case (and presuming the events occurred as described in the article):
* Gerwing's alleged shooting of Allred was almost certainly unlawful; thus, the attempted murder charges
* Kendall's shooting of Gerwing was NOT unlawful; thus, no criminal charges