— they were just locked to his old ARL session. The new laptop had created a new ARL with no playlists. By using the old ARL (which he had saved in a text file before his hard drive died — now he knows to do that), he could still access his original library.
The Deezer ARL token works by authenticating requests made to Deezer's API. When a developer registers for an ARL token, they're essentially requesting permission to access Deezer's servers and retrieve data. Deezer then issues a unique token, which is used to authenticate subsequent requests. deezer arl token link