Here’s how I understand it: at the time, he thought the penalty was for braking under the safety car, which he thought was bullshit considering how many times Max slowed down just before restarting a race, in the past. He didn’t hear that the penalty was for “erratic driving”.

So, thinking the penalty was bullshit, and that the team were challenging it, he figured he was owed the lead once it would be overturned.

That’s how I figure his reasoning, anyway.