Non-reaction-seeking body language is body language that does not visibly ask the other person or an audience for a signal that your message has landed as intended. It reads as confident because it implies you already trust your version of events; the counterpart, reaction-seeking body language, includes tells like raised shoulders with revealed palms ('I'm overwhelmed, what do you want me to do') or repeatedly scanning onlookers' faces for a reaction — e.g. checking a jury's expression, or glancing around a group right after telling a joke.
Seeking a reaction from others does not mean someone is lying, but it does demonstrate a lack of confidence in how a statement will land. The palms-up gesture is fine when subtle and only reads as pleading when exaggerated — this is a matter of degree, not a binary tell. See Body Language Reveals What Words Conceal and Body Language Follows Belief (Indirect Coaching) for related body-language signals, and Embrace Silence / Self-Granted Pause for a verbal-channel analog (not filling silence to seek reassurance).
Source: analysis of Johnny Depp's courtroom demeanor in the Depp v. Heard trial ('5 Key Habits For Unshakeable Confidence').