>>24658871He doesn't mention it because it's irrelevant to the plot and tossing in a "I met it once" line and then never mention anything more about that former meeting is just going to be confusing for those that didn't see that other movie.
Instead, they make him react in ways that makes it clear he remembers them IF you're familiar with their previous meeting, but isn't going to necessarily look that way if you aren't.
Also, did the dub cut or rewrite the bit where he recognizes the shape of Barza's Arceus pendant?