It's fine. ^^ Explanations can make it less fun, but it's more frustrating when you're left out of the joke.
Basically, the Move Deleter just told the trainer his job and boasted that he could help out by making the kid's pokemon forget any move at all. Pretty great, huh? Look at how useful he can be, freeing up those move slots. So, what's that one move the kid wants Slowpoke to forget?
Amnesia. A move based on forgetting moves.
Um... hold on a second. The Move Deleter can figure out how to do this. Probably. Just- just give him a moment, he really can be useful and impressive, honestly!