

It’s considered an herb because the vegetation dies back after fruiting, instead of remaining persistent. If you really want to get technical it’s a forb, which is an herb that isn’t grass-like. But yeah, it’s literally just a description of its growth habit. I don’t think I’ve ever heard someone casually calling a Wisteria a “liana” , for example, because it’s not really a helpful term outside of certain botanical contexts
I was agreeing with you that it’s silly to correct someone calling it a tree outside of specific contexts, just like arguing a tomato isn’t a vegetable.
For what it’s worth, I have had to learn the growth habits of plants in ecology classes for a degree that I am currently earning. I have plant identification books that use those terms, because they do have a technical use.