I hear him stopping the tape in the middle of the line "because I'm so strong," also throwing the tape on the table & walking away. I DO think you got that part right. I think the implication is that ayu is self-deluding, saying she's "strong." That's why the song stops suddenly there, cuz it's an interruption to keep her from lying to herself anymore.
But I hear "yeah right" thickly accented like the others do, probably because I read that meaning into it.
