I think that’s taking that line at face value when it’s very clearly not literal, but delivered in a wry, amused fashion. Leia is not literally telling Rey that she shouldn’t underestimate BB-8’s abilities, nor is she repeating it on the skiff as if BB-8 has proven her wrong.
I get what you’re saying but to me it just seemed like a setup to a “cute” moment later on in the film.