Is it true if a let serve hits the non receiving player standing in the non service court, this is still considered a let serve and taken over? If so, why?

Whether a a let serve in the game of Pickleball hits the non receiving player standing in the non service court is reserved depends on whether the ball made contact with the court. If it did not make any such contact, then a hit to the standing player would count as a let save and would be reserved.

Because these rules in Pickleball are complex and not immediately obvious from a common sense point of view, it is well worth having a classroom session showing the positions and tactics as well as the scoring system before players go onto the court.