Secrets are not a secret anymore if more than one person knows...
Owen's comrade might not have been interested in taking the risk.
Not really. See below.
Restated,
One morning he looked out to his garden and saw a Yankee soldier destroying the crop. He told the soldier to take what he needed, but not to destroy the rest. The soldier told him what he could do with his garden; so Stephen shot him.
[ETA - note the time-of-day discrepancy, morning in the familial account vs evening in the newspaper clipping]
The more I read of this, the more my opinion of PTV Owen is that he was a complete idiot. In fact, I'll wager $20 that if the complete Provost Marshal report is ever discovered we'll find that PVT Owen had a habit of being a discipline problem.
Think about it -
A) he's out sneaking around doing things he shouldn't be doing and
B) when discovered, doesn't light out and head for his bunk.
C) When told to just take what he need (indicating that Ball showed sympathy), Owen instigates things with his obviously rude replies.
D1) Whether Ball shot Owen out of pride with both barrels of a shotgun (ergo, two shots quick), or
D2) whether there was an exchange of shots (one empty chamber in Owen's revolver, with Ball returning the compliment),
PTV OWEN put himself in this stupid situation.