Is 'bouncing' an airliner on landing in high winds a deliberate technique, or something always unexpected?
Bouncing a landing is neither intentional nor desirable. There are several reasons why a student pilot might bounce, but for a professional pilot, it's most likely related to wind gusts, which are a challenge no matter how much training and experience you have.

Gusts are by their nature unpredictable, and if one hits the plane right as it's touching down, it can suddenly lurch upward and/or downward, resulting in a bounce. That's probably also why your plane was "rocking" before landing.