"Homicide" isn't a criminal charge in Texas. From the jury charge:
"A person commits the offense of murder if the person 1) intentionally or knowingly causes the death of an individual or 2) intends to cause serious bodily injury and commits and act clearly dangerous to human life that causes the death of an individual.
"Our law provides a person commits the offense of manslaughter if she recklessly causes the death of an individual. A person acts recklessly or is reckless with respect to the result of her conduct when she is aware of but consciously disregards a substantial and unjustifiable risk that the result will occur. The risk must be of such a nature and degree that its disregard constitutes a gross deviation from the standard of care that an ordinary person would exercise under all the circumstances as viewed from the actor’s standpoint."
Guyger testified that she intentionally caused his death. She wasn't acting recklessly, she didn't "consciously disregard" that he might die as a result of her shooting him in the chest. Her testimony is that she saw a man, pulled her gun, took aim and shot him dead. Her confusion about where she was doesn't come into it. Her own testimony took Manslaughter off the table.
Trouble with this is that it's factually not true. In Texas, numerous individuals have been shot and killed without it being "murder."
Therefore, the simple act of intentionally killing someone cannot be murder, because the reality that this happens quite a lot without resulting in murder charges, contradicts the asserted definition.
Murder cannot be defined this way because it factually contradicts known facts of people killing other people and no charges being filed against them.
You cannot have inconsistency in law. Either you have to charge and convict everyone who kills someone with murder, or you have to use a definition for murder that allows for "killing with intent" exceptions.
But inconsistencies and contradictions seldom seem to slow down the courts anyways. They just go on full speed ahead with whatever they prefer to believe.