what happened to this beer?

I wasn't implying that you did it, what I meant was who had the bottle before you did, could have happened in shipping or if it was stored in a box upside down in the back of the bottleshop. The reason I stated this is because this looks like the sediment that is in sparkling wine (champagne) because it is stored upside down and then degorged to remove this sediment and replace it with a small portion of wine.

 

That's my guess - a case ended up upside down and the freight shipper didn't care. I've had a few bottles where that's happened - I usually just carefully wipe the neck with a clean towel to avoid as much of the sediment/gunk as possible, and pour normally.