How could Anne be sure that CW had no idea that his remarks would be repeated back to her? From her POV and in her present state of mind, I get the impression that she'd be convinced that he either hoped she'd hear about it (because he was still angry and wanted to get back at her) or that he didn't care whether she heard or not (because he no longer cared about *her* except for being glad to get out of a relationship with a woman who had aged so quickly).

Then, the ON tells us directly that "in the first moment of appeal, he had spoken as he felt". How could Anne know that for certain, either?

In fact, I find that JA changes perspective twice in 2 paragraphs. The previous 2 paragraphs are Anne's POV. The beginning of the paragraph you quote is the ON speaking, but at the 4th sentence in, she changes unobtrusively to 100% CW's POV, IMO.

He had not forgiven Anne Elliot. (I think that's still the ON, stating the facts.)

She had used him ill, deserted and disappointed him; and worse, she had shewn a feebleness of character in doing so, which his own decided, confident temper could not endure. She had given him up to oblige others. It had been the effect of over-persuasion. It had been weakness and timidity.

This is no longer the ON speaking, but CW's own feelings. Clearly, *Anne* does not feel that she has "used him ill" - she feels she probably did him a favour by not saddling him with a wife at the time. You might read it as Anne's interpretation of CW's feelings, but IMO, this is one time that we see things from inside CW's head.