Was there a need to cuff the guy at all? If it can be shown that they don't normally cuff white people in the same circumstances then that itself would be a thing that comes up in the trial.
I mean, the guy was just asleep in a car then they've charged him with drunk driving, already questionable. Then, the guy was already complying with them, and they went to cuff him. Already at least two questionable points here, and it's about the entire event itself, they pretty much concocted the whole reason to interact with a random person, and kept upping the stakes. And the guy might well have feared what would have happened to him in custody. People do die in custody or in the back of police vans. Black people, that is.
So while you might say it's reasonable to just go along with them, that's also coming from the point of view of someone far less likely for them to fuck with once you're in the system. They're just hand cuffs right, what's the big deal? Well clearly if they're cuffing you, the goal is to stick you in a prison cell, and who knows what the fuck will happen to you then, especially a black person in the south. If they lock him up, then he's gotta wait for a bail hearing before he can get out, and how long does it take to even schedule a bail hearing, and can these be delayed?
And even then, after the bail hearing he can only get out if he can afford being shaken down for money. Meanwhile, he's lost his job, lost his car, probably lost his relationship, possibly lost his kids, who knows. If he can't afford bail after the bail hearing, then he's stuck rotting in prison until his low-priority case can be heard and he's being represented by some snotty underpaid and uninterested public defender, and assuming the public defender doesn't blow the case, the best he can hope for is that the judge just dismisses the case and he's free again, in 9 months or something, and he's ended up doing almost a year in prison and losing everything, over something that's not even a crime, based on the cops say-so, rather than a judge. And the cops involved knew all this even before they charged him.
That's the end result of targeting people like this for the "letter of the law" where they'd let it slide if he wasn't black in the first place.