Monsieur Lucien

So the older gentleman who comes to see Antoine at the printing shop, he was supposed to be the guy Antoine saw kissing his mother when he (Antoine) was playing hooky with René? I found it confusing because it was a different actor and they didn't really look alike. He was never referred to as "Lucien" in The 400 Blows, was he? Julien Bertheau, who portrays him in Love on the Run looks more like Albert Rémy (who played Antoine's father) than Jean Douchet (who played the lover). It's fine, I understand that sometimes you can't find the same actor, maybe Jean Douchet was unavailable or unwilling to work for Truffaut in 1979, but then why use the old flashbacks with a different guy who looks nothing like him?