Success Exchange versus getTokenSilently

I see that after every Success Login or Success Silent Auth
there is a Success Exchange in the log for Authorization Code for Access Token

looking at the quickstart for angular the example of getting the token to call an api suggests implementing a call to client.getTokenSilently using the normal Observable construct

So why are there two different things, and if the Success Exchange has already happened shouldn’t I already have the access token in the browser somewhere? If so how do I “get in front of this call” to get the access token? I don’t see where this is getting triggered from on the angular side ?

ok i get it now, make the call and the lib will determine where to get it from