I think the schematic and the layout show the same thing, but in a different way. I could have made an error though, I do that a lot.
The center of the input jack gets wired to the sleeve art of the input jack which goes to ground. You are correct in that this is to ground the input when there is nothing plugged in.
The center of the boost switch also need to be grounded. It is convienent to use those pins on the input to ground it. Its confusing because it makes it seem like those parts are intricately related but they really are not. The center to ground on the boost switch is really the ground path for the cathode of the first tube stage. Since the switch is center off, you are either grounding the 1.5K resistor alone, or the 1.5K resistor and 25uf capacitor in parallel, or the 1.5k resistor and the .47uf in parallel.
The input wiring always seems to be a bit confusing. I’ve attached a couple more pictures to show how it is supposed to wire up. The second image shows the 1M resistors to ground for the pop supression too.