That is the difference, in terms of information, between constitution and communication.
Intrinsic personality is an assemblage of constitutive information, a kind of library of possible behaviors, grouped around a core of identity.
Extrinsic personality is how this information is communicated in each context. This aspect of the information no longer depends on the transmitter but on the receiver.
The information provided by a person serves us to represent them (as an extrinsic personality). So it reflects our mentality more than his, at least at the beginning. It takes a long evaluation of one's behaviour in different contexts to have a less approximate idea of one's (intrinsic) constituent personality.