So the example you made in Procreate is going in the right direction, but the thing to keep in mind is that it's not enough to take a texture and simplify it into a 2D pattern that can then be repeated mindlessly as needed. A repeatable 2D pattern would have to ignore the variation in surface orientation of the object upon which the texture rests, and the relationship each individual textural form being implied has with the light source.

I have a bit of an explanation I wrote up for another student that may help... or may just make things more confusing. So before I share it, I'll state this - what you've drawn there is a step in the right direction, as you're focusing only on implicit markmaking, using cast shadows. Even if the cast shadows may or may not be 100% correct based on the forms casting them and all the variation I mentioned, by focusing on drawing your cast shadows this way, you'll gradually develop a more "correct" understanding of texture, and that'll be refined as you continue to practice it. What matters is going in the right direction, which the previous approach of employing explicit/constructional markmaking was not.

The explanation hinges around this diagram:

In the top, we've got the structural outlines for the given form - of course, since we want to work implicitly, we cannot use outlines. In the second row, we've got two options for conveying that textural form through the use of filled black shapes. On the left, they fill in the side planes, placing those shapes on the surface of the form itself, and actually filling in areas that are already enclosed and defined on the form and leaving its "top" face empty. This would be incorrect, more similar to form shading and not a cast shadow. On the right, we have an actual cast shadow - they look similar, but the key point to pay attention to is shown in the third row - it is the actual silhouette of the form itself which is implied. We've removed all of the internal edges of the form, and so while it looks kind of like the top face, but if you look more closely, it has certain subtle elements that are much more nuanced - instead of just using purely horizontal and vertical edges, we have some diagonals that come from the edges of the textural form that exist in the "depth" dimension of space (so if your horizontals were X and your verticals were Y, those diagonals come from that which exists in the Z dimension).

As to your other question, the point of the distinction about grooves/holes/etc. is that you still need to be focusing on the fact that the marks you're drawing are cast shadows, and that they are resulting from the textural forms that are present. Correctly identifying what those textural forms are (and not thinking of the grooves themselves as the textural forms, or the things you actually draw) is the key here.

So simply wrapping a bunch of cross-crossing lines around your tire and then fiddling with line weight would be incorrect, because no part of that actually involves thinking about how the textural forms at play relate to the surfaces around them.

While the result may still be the same in some cases, or pretty close in others, the point is that this is an exercise that is focused on getting you to think about those spatial relationships. The end result doesn't matter, it's the approach you use to get there and how it forces you to think. The goal is the same as it is throughout the rest of the course - to rewire how your brain thinks about the things you're drawing, as they exist in 3D space, and not to simply regard them as the lines and 2D shapes that ultimately result and make up the drawing.