Interesting punctuation

Came across this in Silver Borne by Patricia Briggs, in the heroine's viewpoint. A private detective is guarding a  client. He says on the phone:

"I'm kinda hoping her soon-to-be-ex shows up," he said softly; I thought so she wouldn't hear him.

Semicolons always seem a bit academic and formal to me. Most times when I see one in popular fiction I feel it could be advantageously replaced by two sentences.
Fr'instance:

"I'm kinda hoping her soon-to-be-ex shows up." He said it softly, probably so this client wouldn't hear him.

But .  .  . though my editorial alternative might be slightly clearer,  Briggs' choice — or her editor's choice . . . this 'feels' like an editorial correction — is maybe the better writing. It uses POV so neatly.