What is this type of monochrome called?

By changing the Mode to Lab Color,  then slowly and methodically dragging the mouse across the the image, typewriter style, while watching the Info panel, there is an interesting result.

As you know, plus readings in the  a  channel would indicate magenta, minus values would indicate green

In the  b channel plus readings would Indicate yellow and minus values would indicate blue.

In other words, if, at any point, a minus number appeared in either the  a  or the  b  channel it could indicate more than two hues appear in the image.

All values were plus.

From that you may assume that, besides magenta and yellow (to create the red) no other hues, were used. In terms of tonal scale (black), the black is easy to see. White was applied below the right eye since it is lighter than the paper.

NOTE: There were points where  a  registered zero -- meaning yellow was the only hue at that point  -- but they were miniscule and I assume they may have been the result of a minor variation in the scan.

Use duotones in Photoshop

Monotone = 1 ink

Duotone = 2 inks

Tritone = 3 inks

Quadtone = 4 inks

This is not a Monochrome

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Even when it's not excessive colourful, it's not monochrome. I see at least 2 colours: red and black, if I do abstraction of the background.

To do that in Photoshop, you need to have chalk-simulating brushes, a tablet and some drawing talent. It helps to know how to do that on paper in the real world. Well and then you could simply draw and scan... , but for some applications, that will not be suitable.

RGB color mode.

What exactly are you trying to emulate – just the colors or also the linework?

That is a color photo of a drawing done on a textured paper.