Kölsch is actually a weird one. It's true that Kölsch is an ale and Kölsch yeast is a top-fermenting ale yeast, however the style also calls for lagering the beer at cooler temperatures at the end of fermentation, which is the same process that all true lagers undergo. This is why Kölsch has a clean lager-like taste, and is often mistaken or debated as a lager.

See also: California Common / Steam Beer, which is sort of the opposite case (lager yeast fermented at ale temps)