So if the DM says that the NPC is acting fidgety while saying something, what does that mean? Because as I just said, that can be interpreted in several ways.
Which is why making an Insight check is good, because then we can straight-up learn, with minimal ambiguity, that we (the PC) feel that the NPC is being evasive. I as the player don't have worry that I'm gotten what the DM may or may not have meant to be a clue, and I as the DM don't have to worry that my players understood my hints. (This is doubly true for me because I'm an aspie and sometimes don't read people well.)