When you view passwords in Orion, you are also viewing passwords saved on Keychain, just in this case Orion's bucket.

There are various system API's that allow apps to read from each other's bucket (obviously all Apple apps have access to Apple's keychain bucket). This is how you can autofill passwords from different keychains in Orion (for example Apple's - which I call Safari's because this is how typically passwords land in it).