That's not what happened. It was in-car early voting that was being contested. But like others on this thread, it isn't clear to me what the controversy is.
How did it work? Did they drive up to a box or hand the ballot to a poll worker? If it was just dropped in a box then it seems no worse than mailing or other drop-off methods. Once poll workers are in the chain of custody, things get out of hand (and into a dumpster), especially in heavily dem areas.
Basically, the Texas Elections Code requires that in-person voting occur at a “voting station” in a “polling place,” and the plaintiffs argue that the voter’s car does not qualify as either.
While I can think of some practical reasons why in-car voting presents a risk to the integrity of the election, the plaintiffs don’t make those arguments. They rely purely on the language of the statute.
While I think the plaintiffs have a technical legal point, I think they’re making a mistake from a strategic and political standpoint. This is making Harris County republicans look bad, and there’s a good chance that the votes at issue favor Republicans anyway.