OK, I've looked at Wikipedia's records list and I see why that is. It's because they consider Dragon Mountain at Marineland to have been the previous record holder (for "complete circuit" coasters, as there was actually a 200+ foot shuttle coaster that predated all of them). This is actually a complicated issue and relates to the distinction between "tallest" and "tallest drop" that you mention. Dragon Mountain has a longer lift than GASM, and a greater elevation difference between its highest and lowest points. But DM is built on the side of a huge hill, and so it never gets as far off the ground as GASM. Furthermore, its biggest drop is only half of that height, or less. I rode DM long before I would ride anything else above 100 feet in height. To my mind it isn't really a tall coaster, despite the epic lift chain. (It is, however, a strange and unique coaster for various reasons, and I am quite fond of it.)