Fix uvm 368 (#675)

* fix copy and paste error

* improve wording

index.bs

@@ -3530,7 +3530,7 @@ This [=registration extension=] and [=authentication extension=] enables use of
 :: The Boolean value `true`, encoded in CBOR (major type 7, value 21).
 
 : Authenticator extension processing
-:: The [=authenticator=] sets the [=authenticator extension output=] to be a user verification index indicating the method used
+:: The [=authenticator=] sets the [=authenticator extension output=] to be one or more user verification methods indicating the method(s) used
     by the user to authorize the operation, as defined below. This extension can be added to attestation objects and assertions.
 
 : Authenticator extension output