Hard to tell from the picture, but, yes, I would suspect it's not leather also, I have seen boxes made from that weird fibre board, I think it's cardbaord soaked in phenolic (bakelite) and hardened. It was one of the first synthetic composite materials and people tried to use it for just about everything. It's the same thing heater boxes in old cars are made out of, before they discovered fibreglass...
pick off a tiny fragment and hold it in a lighter, if it smells like a cow is on fire, it's leather, if it smells like your car is on fire it's fibreboard...
[There are a few other weird things that were used, asbestos instead of paper, rubber compounds, and certain weird tree sap's that harden...]
As to the box, I have seen old ads for inexpensive machinists tool boxes, never occurred to me that someone might be making them out of something other than metal.
Will have to pay more attention to the ads...