Because he's charged with 35-42-1-1(2) which is felony murder. I don't know why people are saying it's NOT felony murder when it is the literal definition of felony murder. The difference is the intent element.
Under this statute, for (1), you need to prove the mental state of "knowing or intentionally" killing another person.
For (2), there is no intent element. The law states that a person who kills another human being during the commission of the listed felonies is guilty of murder. That's what "felony murder" means.
"Felony murder" is not a separate homicide charge like manslaughter or reckless endangerment. It is murder but it does not require an intentional or knowing mental state.
Again, the point behind this is the state is saying that by engaging in these listed violent felonies, if someone dies, we are going to hold you responsible without having to prove intent. Your conduct by engaging in kidnapping or burglary or arson or child molestation is so egregious, if someone dies, you are as responsible as if you intended it.