Definition of "puzzling"

Sunning himself on the board steps, I saw for the first time Mr. Farquhar Fenelon Cooke. […] A silver snaffle on a heavy leather watch guard which connected the pockets of his corduroy waistcoat, together with a huge gold stirrup in his Ascot tie, sufficiently proclaimed his tastes. […] But withal there was a perceptible acumen about the man which was puzzling in the extreme.

1897 December (indicated as 1898), Winston Churchill, chapter II, in The Celebrity: An Episode, New York, N.Y.: The Macmillan Company; London: Macmillan & Co., Ltd.