TVP is rather cheap type of soy* because it's what leftover from soybean oil extraction. It's pretty protein dense because of that so recipes like this add moisture to it to help make it a little softer. It's very yummy when seasoned well!

* TVP itself technically stands for textured vegetable protein, but it's 99.9% of the time always soy unless specified otherwise (it technically can be made from other plants)