This might be something that the lesson doesn't explain well enough, and I'll be addressing it when I update the material (currently I'm working through producing new stuff for Lesson 0, then after that I have to update Lesson 1's boxes section... but I'll get there!)

Basically, the texture exercises are not about just drawing what you see. I think a lot of students get confused on that point, and they interpret the instructions as specifically identifying shadows in their references and then copying them over. That is not the case.

Instead, we first observe our reference in order to identify the actual textural forms that are present - then using that information, we design a shadow shape in our drawing that establishes the relationship between the textural form, and the surface around it. While this shadow may well be the same cast shadow that is visible in the reference image, that isn't a given - rather, the shadow needs to be developed based on your understanding of how that little form exists in 3D space.

To answer your actual question though, the only thing you draw for the texture analysis exercise are cast shadows. No form shading (which as explained here will not be playing a role in any of the drawings we do for this course), not local colour, not outlines of the forms themselves - just the shadows they cast. And as such, there's no grays to worry about - no intermediate values. Just straight black, because cast shadows occur where the light is actually blocked by a form from reaching another surface, and for the purpose of keeping this as simple as we can, we're drawing as though there's only a single light source.

This is still difficult, even with these misunderstandings clarified, and students are still not expected to be able to necessarily succeed at this exercise. It's just an introduction to the idea of using implicit markmaking to convey the presence of textural forms. So, based on the information provided, give it your best shot, then continue on.

Oh, one other thing I should mention - the first texture being crumpled paper is something that was added after the first revision of that exercise, and it has been both immensely helpful, and for some people, also kind of confusing. The reason it's helpful is that prior to its addition, students were very hesitant to actually break their textures into a series of pure black and pure white shapes. The crumpled paper texture basically gave you no option but to work in large black/white shapes, and forced students to be bold. Having done that, they tended to go on to the other two rows doing a much better job, pushing their shadow shapes further than they otherwise might have done.

But it's also confusing because despite its incredible usefulness, it also goes right ahead and breaks that core rule of "only work with cast shadows" - since the crumpled paper is almost entirely made up of form shading, with the different facets of the paper differing in value based on their orientation relative to the light source. Those facets that face the viewer are lighter, those that face away are darker. Not everyone realizes that (and those that don't tend to have a much easier time doing what the exercise asks so I'm often hesitant to draw attention to this), but it does mess with those that do realize it. This is something I hope to address in the next revision of this exercise - but for now, think of that crumpled paper texture as a special case, where you only need to focus on breaking it up into shapes that are either completely black or completely white - for that one, don't worry about the distinction between form shading and cast shadows, and again - just focus on doing your best, then pushing onwards.