There’s really only one way this story works, and that’s if Bruce is using Penguin’s scheme as a contrivance to get Waynebeau into the Bruce Wayne Handicap without it looking like a conflict of interest.
Or maybe he just really hates the Bruce Wayne Handicap and wants to make a laughingstock of it.
Seriously, why else does he do anything he does in this episode? He had, like, a dozen different opportunities to stop Penguin, most notably when he steals the folio from the library and just walks out. For that matter, he says that he knows where Penguin’s hideout is—not that “Penguin’s Bookshop” is a particularly difficult “secret” hideout to locate, all things considered. Penguin already tried to blow up a library. There really isn’t any need to wait on a bigger plan because no fraud he could commit at the racetrack would be a nastier crime than trying to blow up a library.