Yes, that is 2FA, two factor authentication, in this exchange instead of a google number generator, it uses a password. So, for example, let´s say you are using the same password for you gmail account. Someone hacks the google servers and sells all combinations of user/passwords on the dark web.

Then some dude out there starts trying users / passwords in cryptopia and bingo! Your mail/pass are the same and he cleans your whole account. If you have a PIN, you have at least a second line of defense.