He might have been exaggerating though, as he usually does...
Actually now I just realized that this comic series doesn't quite jive with the animated series continuity.
This obviously takes place before the "Starcrossed" episodes (Hawkgirl is in her OG costume and no mention of JLU members), and until those episodes Flash had no idea that Bruce Wayne was Batman. But in this one they're all hanging out together in their civilian identities already