NVIDIA refers to 2-way SLI throughout their guide
here which makes me think that the title should reflect that. I was a bit confused by the title personally and while I was anticipating it to be about 2-way, I had initially considered the title to be a typo. The control panel may just say "SLI" for 2 cards but that doesn't mean that SLI by itself must be 2 cards. Before 3-way and 4-way existed, there was only SLI in the control panel. When the control panel was extended to include 3-way and 4-way they most likely just didn't bother to rename "SLI" to 2-way SLI.