If you are summoned as a witness, then you must appear when summoned to do so or face possible contempt of court. You must testify, unless you have a privilege from doing so, such as self-incrimination or spouse. However, you are not required to speak to anyone else.
How the parties and attorneys in a case conduct themselves is up to them. There is no law that requires good manners. Either we learned them and follow them, or we don't. You can wonder all day long about another person's motives, and that includes attorneys, but you cannot read another person's mind. Sometimes lawyers do not have good judgement and tact.
