Who knows what the business owner told the cops, but he could make a case that a casual check told him an intruder was likely on premises, he armed himself after this discovery, and when confronted, the intruder became a threat.
Proximity and ability are there, assuming there is no big physical mismatch in the business owner’s favor. I’d wager the cops heard something that makes the intent component dodgy. Even something as simple and natural as saying “get out our I’ll shoot” when you’re blocking the only exit could cause all kinds of legal problems.
The story says he was shot through the shower curtain. To become a deadly threat he would, at the minimum, have to get out of the shower. I don't think this one is that subtle.
The guy probably thought he'd be OK legally because it was in his house, and the media keeps portraying every potential self-defense case as if it's free for all. But he was wrong.