It seems to have two recipes. One requires a pumpkin, the other does not. The recipes are otherwise identical. Is there a reason for this?

I can confirm that indeed, there is a second recipe. To the best of my knowledge, the resulting red string is identical to the one created via the recipe without the pumpkin, so I am also curious as to why this second recipe exists.

Edit: I did a quick search for the recipe, hoping to get some clarification.
https://github.com/Vazkii/Botania/blob/c904244bcc9a557f4d96a5600a24e6b32b9c4e34/src/main/java/vazkii/botania/common/crafting/ModCraftingRecipes.java#L1468
There is a comment there asking, "Are you in a pinch?" but no further clarification.
So... I'm still confused.

It says "in a pinch?" In the code comments. Wat
On Tue, Dec 22, 2015 at 8:59 AM Wouter van den Heuvel <
[email protected]> wrote:

I can confirm that indeed, there is a second recipe. To the best of my
knowledge, the resulting red string is identical to the one created via the
recipe without the pumpkin, so I am also curious as to why this second
recipe exists.

—
Reply to this email directly or view it on GitHub
#1679 (comment).

It seems that "Are you in a pinch?" is simply the line of text from the Lexicon entry. Still no idea about the pumpkin, the recipe in the book doesn't require one.

According to the red string article on the official FTB gamepedia, it's a reference to Pumpkin from Akame ga Kill!.
It's one of many Botania's Easter eggs.