Robert Grant Burns himself had mentally called it a hummer.

He did not reply to Jean's tentative apology for her own plot-idea.

He was thinking about the idea itself.
Robert Grant Burns was not what one would call petty.

He would not, for instance, stick to his own story if he considered that Jean's was a better one.

And, after all, Jean was now his leading woman, and it is not unusual for a leading woman to manufacture her own plots, especially when she is being featured by her company.