Well, that’s because the recipe accepts threads in general; not specifically the Spool of Thread.
Right now there’s only that one kind of thread, but imagine there are more kinds of threads in the world. You can then craft the Bolt of Cloth using any of these threads.
Maybe it should read “Any Thread” or something similar so it is clear that it’s a general item rather than a specific one?
At least part of the problem is that the icon is exactly the same as the specific case too. The best result would be if the tooltip of any generic item expanded out to show the icons and names of all the specific items that fall under the general heading.
Starting to go into suggestions territory, but the devs have been working on how to make every part of the game clearer lately.
The tooltip is for the resource itself. People kept wondering why sometimes wool was being used even if the icon showed a silkweed bundle. Well, that’s due to the tags on the item itself.
You see “wood” on the ingredients from the carpenter. Have you wondered why it’s not “Oak log” or “Juniper Log” too? 
I’ll move this to suggestions, it’s not a bug. What is really difficult sometimes is to find a generic icon for the represented resource. Sometimes it’s straightforward, like “Mean Bed” as ingredient for “Comfy Bed” but other times is a generic resource, like fiber, thread, wood… And the icon might confuse people, thinking that the ingredient itself has to be the exact one as in the icon.
How about a tree icon for wood? That sounds generic enough and isn’t a representation of a specific block. That was my first thought anyway.
It can be the same icon, but a different frame (e.g. bold blue frame, or glowing frame), that will mean it represents a group of items, and tool-tip to show which items fall into the group. Clicking on it to bring a drop down of all options, and let me select the one I want to use for the job (show inventory counts as well in the drop down in front of each item).
Selection is optional, making the game decide which one to use from inventory.