In the info box photo on that page, only the box at the bottom (with the red and purple switches) is the processor; above it are two blanking plates and a TU-56 tape drive. I suspect that KPS considers the machine to just be the processor, whereas you're looking at the processor and surrounding peripherals.

That said, there were PDP-11's that were desk-sized, such as the DEC Professional (about the size of an IBM 5150), or even smaller, the VT240 (which is largely an embedded PDP-11, and it has about the footprint of a C64, though somewhat thinner)

PDT 150 was a desk top model - pdp11/03's where targeted at labs and originally came in a wheeled trolley about half cab height that you placed an VT52 or VT55 on top.