I apologise if my reply was confusing.
To clarify: your iPhone and Apple Watch are treated entirely independently for Apple Pay. Your post indicated that you perhaps expected otherwise ("why aren't they syncing?").
You can add cards to Apple Pay on your iPhone via Wallet on your iPhone.
You can add cards to Apple Pay on your watch via the Apple Watch app on your iPhone.
Adding cards to Apple Pay on one or the other device does not automatically add them to the other device.
Each separate combination of card + device is given a unique Device Account Number. This is why, for example, you can leave your iPhone at home and turned off, but still go somewhere else and pay using Apple Pay on your watch.