It happens that he simply uses an application called Authenticate.app located in the extension folder and a simple command allows you to have access to your username and password:

./Authenticate.app/Contents/MacOS/Authenticate -get username moystard

Replace username by password, and tada, you get the password.

Not saying here that you should not use Alfred extensions, but it is good to be reminded sometimes that something that is initially convenient also leaks your precious credentials to a third party.