Look at the start of the video. You can see clear skies in the left 1/3 of the screen. The crew said it was a very rough ride down final, with a big direction split with winds aloft from surface winds. I don't know what was showing on radar, but I've had a small, innocent looking rain shower set off the wind shear warning in a 737. Near BOS one day I had a shower that wasn't more than 1/4 mile in diameter send out a bolt of lightning. Definitely got our attention.