The camera is still pretty aware of which lenses are designed for crop sensors and which cover the full frame, even from third parties. EF-S and EF are actually identical in every facet except for the physical protrusion of the rear element. Whether or not the camera can detect it is something that the lens or camera is aware of via firmware or database. For example, the sigma 18-35 forces the camera into crop mode and uses a regular EF mount, not EF-S.
Because it's not a fully manual lens, I would be about 99% sure it would crop automatically.
