[JorgeGT]

Being outside the business, I found it surprising as well! The fonts are named GuardianTextWeb, GuardianSansWeb, etc., suggesting to me they have been purposely commissioned by The Guardian to obtain a differentiated look and feel.

However the license is non-exclusive and revocable, and restrictive to the point that only web seems to be allowed. The fonts are indeed available for purchase: https://commercialtype.com/catalog/guardian which from the point of view of protecting the look and feel of your brand that you just commissioned seems a bit weird.