Who’s right and who’s wrong?

Long story short, my 5yo caught an attitude when asked to turn down her tablet. Her stepdad called her over and calmly tried to calm her down. The whole time they were talking, she was bent over with her head up, leaning on the couch. He told her to stand up straight multiple times and she didn’t listen ofc. He asked her why and she said “because I don’t want to listen to you.” So he took her tablet away and told her she can’t stay at her grandmas house tonight (she usually sleeps over on fridays.)

I’m not disagreeing that she needed some sort of consequence but is telling her to stand up straight a sign of respect? He told me that was very disrespectful of her to not stand up straight while he was talking. Is that too much or am I over thinking?