Cylinders, by definition, don't taper. So I would argue that describing the building as cylindrical is no more accurate than describing it as spherical. The Sugarloaf project is actually a hemispherical dome with the ramps wrapped around it.

I'm surprised you didn't take Kaplan to task for a much more egregious error, which was to suggest that the Guggenheim museum led to the creation of other "spiraling" buildings like Mies' Neue Nationalgallerie and Pei's East Wing, neither of which have any relationship at all to spirals.