Urbit is an OS, apps have access to whatever you give them access to. If you want one app (say, a dating profile) to not have access to data stored by another app (say, your bitcoin wallet), you run them under separate sub-identities as described above.
That has nothing to do with the thing you quoted ("network identity and keys are already baked into all your interactions with the network"), which describes how urbit nodes talk to each other. Whatever identity you run an app under, all traffic from that app will be cryptographically signed by that identity.
That has nothing to do with the thing you quoted ("network identity and keys are already baked into all your interactions with the network"), which describes how urbit nodes talk to each other. Whatever identity you run an app under, all traffic from that app will be cryptographically signed by that identity.