Samantha's Witchcraft Blows a Fuse - S8-E25
Other mistake: When the police pull up outside the Stephens' home, it is a set shot with fake background. The "road" doesn't match the outside of Stephens' neighborhood shown throughout the series with the Kravitz house across the street (and not a pine tree forest as shown here).
Answer: Larry had been telling Darrin what it means psychologically that Samantha gave the coat away. Larry said giving it away meant she's happy being married but if she liked the coat it means she desires to be single and carefree. So when Darrin sees the coat, he immediately thinks Samantha doesn't want to be married and the fact that she twitched it means (in his mind) she wants to be a single, carefree witch again.
Bishop73