It is fairly apparent that it became airborne before it was meant to. Think about an aircraft doing, say 40 knots. Stall speed is about, say 60. Encounters a rapid increase in headwind of say, 25 knots. It will fly until that headwind component drops back to say, 15. Then we see the behaviour that others have discussed. What happened appears obvious - it stalled just after lift-off. Until the pilots are interviewed, why it happened is the mystery.
As an anecdote, I have heard of a DC3 becoming airborne with the elevator gust lock still attached. The crew flew it to a successful landing using trim. Don't know whether fact or fiction, but believe it could be done in the right conditions.