So if I had to guess, "Hunger Rate Multiplier" was renamed into "Bed Hunger Rate Multiplier" (annoyingly defNamed "BedHungerRateFactor" because what is consistency) given the similarities in the name and the fact that its in the same .xml.
The pawn stat list was made by copy over all the labels, so its either that or a since-removed stat.
On that topic though, the Sleep accelerator offsets Bed Hunger Rate Multiplier, rather than Hunger Rate Factor. I'd assume its Hunger Rate * (1 + ∑(Hunger Rate Factor Offsets)) * ∏(Hunger Rate Factors) * Bed Hunger Rate Multiplier but I don't know for sure.