Howcho - To elaborate on Mike's comments, the reason for the last step (ie, add a tinge of yellow) is that if you use a B&W adjustment layer, as suggested by Colleague, the result is an RGB image that has no color tint whatsoever. It is pure grayscale. However, your original photo has a very slight warm / cream tint, typical of photos that have aged, so, if you want to reproduce that look, you have to take an extra step to uniformly add the cream tint to the entire print. This is what his extra step does, although, the intent would have been clearer if he had suggested using a cream (ie, weakly saturated yellow) layer, not a "yellow" layer at low opacity.
Tom M