Sorry, what was your name again?

I was just watching one of my favourite movies (The Fifth Element) again and this time I noticed a little slip. I don't know if this was on purpose, but when Leeloo and Father Vito Cornelius arrive at Korben Dallas' apartment, the Father addresses him as Mr. Willis:

"I'm really sorry to have to resort to these methods Mr........ Willis [Bruce immediately corrects him "Dallas"]... uhhh... Dallas, but we heard about your good luck..."

I wonder, was that a real slip or did they throw that in there as a subtle joke?