They're really common in Korea, especially the mid-range Escape hybrids, those things sell like hot cakes. Still, when they say the biggest bike manufacturer in the world, they mean OEM manufacturing as well. Giant and Merida, and a few others like Maxway, make frames for a huge amount of bike brands. While Merida own 49% of Specialized and make their bikes, Giant manufacture and assemble/box bikes for Trek, Scott and Colnago AFAIK, and probably a whole lot of other brands.
Giant and Merida branded bikes offer great value for money, though, as compared to some of the other bands they manufacture for, in Korea at least. You can get a similarly equipped bike (an alloy frame 105 specced road bike for example) for a good few hundred dollars cheaper than the equivalent bike from some other brands.