Apparently, you don't understand the meaning of "DSLR". DSLR stand for Digital Single Lens Reflex, which is a digital version of the Single Lens Reflex (SLR) camera. The defining characteristic of a SLR, digital or otherwise, is that it has a single lens that one looks through for both image capture and shot composition which is generally made possible by a mirror that translates out of the way of the shutter when the shutter is activated. Interchangeable lens do not enter into the equation.
The Cannon S5is is, in fact, a DSLR camera.