Why would that be the case? Chardy is an error hitter and most error hitters aren't good against slice and tempo changes. The H2H was also against him.
Petzschner's baseline game is below average, so I thought Jérémy's serve would enable him to maintain serve very easily, while being able to break Petzschner once or twice in the match.
You are right about Jérémy struggling if someone can keep the ball in play with a lot of slices, just didn't think he'd give Petzschner much of a chance to do that, especially not on his own serve.