Anne is reacting to the following from Admiral Croft about Benwick: "a very active, zealous officer, too, which is more than you would think for, perhaps, for that soft sort of manner does not do him justice" when she says: "Indeed, you are mistaken there, sir; I should never augur want of spirit from Captain Benwick's manners"

Then, "Anne was caught. She had only meant to oppose the too-common idea of spirit and gentleness being incompatible with each other, not at all to represent Captain Benwick's manners as the very best that could possibly be". It seems to me she was thinking more of herself here when ostensibly defending Capt. Benwick from the charge of want of spirit. Instead, she was "caught" in appearing to somehow disparage Capt. Wentworth's manners, when in fact she felt the opposite :-)