Not quite. iOS 8.4 entered beta a few months before WWDC with a redesigned Music app that was a pretty clear signal that Apple would be doing something with it later on, but Apple Music itself didn’t launch until June 30, after WWDC, with the public release of iOS 8.4.
As for iOS 9 beta, iOS 8.4 was released roughly at the midpoint between iOS 9 betas; Apple didn’t release a special beta update to launch Apple Music on iOS 9. Apple Music was present in the next beta, which came a week later.
In any case, considering the relatively minor changes involved, I’d say code supporting Apple Card is already present in the iOS 13 betas, but I’ll have to download an IPSW to check.