In post-race interview Leclerc was asked about it, and he stated, that undercut as a strategy option was not discussed with drivers before race. I gather than with Vettel it was a call by pit wall based on in-real time situational analysis Vettel was in (lap count, and traffic around him). I am not sure one could plan for that; it just happened, and Leclerc might not like outcome, but he should realize Vettel is not there to end up off the podium. If he wrote Vettel off, well, now he knows better.