No, you weren't reading it wrong. After a little measuring on the picture and a little math, it seems that they are measuring from the very back of the thumb ramp on the back of the blade to the tip of the blade. Novel approach, no?
A mind all logic is like a knife all blade. It makes bleed the hand that uses it.
I called Alan Harris of Smoking Hole and asked him about the "Mantis" Folding knife he told me that they are still in the production stage and still making small changes and improvements and that changes are going to be made to the web site information and that some minor mistakes were made. The dimensions are:
closed length: 5.560"
blade cutting surface: 4.412"
Back of locking notch to tip: 5.200"
overall length: 9.740"