They didn't make up a "new law".
When you're detained cuffed and frisked is the base line.
He did. He issued what he called a "lawful order" to get out of her car, which seems to be without legal basis. I certainly can't see what valid reason he would have for it. Personally, I think that when armed agents of the state issue orders and enact them by force, they should have specific legal authority to do so, preferably including a court order.
Perhaps there is some legal basis for this under Texas law. But I can't figure out what it would be.
https://www.washingtonpost.com/news...23/sandra-bland-and-the-lawful-order-problem/
Generally, the police are only allowed to detain a person long enough to conduct their investigation. In this case, the investigation was concerning a failure to signal a turn, which didn't yield any evidence of any other crime or cause to investigate further, which therefore should not have required much investigation. I'm not sure why he would have needed to force Bland out of her car, let alone frisk her, for that, and he certainly didn't need her to put out a cigarette. He could have handed her the warning and walked away. He may not have liked her attitude, but that's well within her rights, especially when he asked her specifically about it.