Nice little tutorial - that technique is similar to what is known in the
print business as a duotone - apart from the effect, it can be a way of
getting more dynamic range out of the press.

In Photoshop you use the Image->Mode->Duotone option (only works with a
greyscale image) and then choose how many and what colour inks - you can
adjust the curve for each ink to change how it applies across the tonal
range.