Nope, hadn't got wet. And the horn does still work.
Long ago when it was still under warranty, I had the commonly reported issue of the whole instrument panel going dead, but I had that fixed by the dealer so I'm assuming it shouldn't be a problem with the connections.
I did find some old posts - one said try pushing the corners of the instrument panel (didn't fix it - like I said, shouldn't be a connection problem) and another said it might be the Airbag Control Module. I guess that warning light does throw error codes, so that's probably my need step to see what codes I'm getting.