I am confused about the length of a tourist visa in China.

Bruno, generally speaking, an L type is valid for 90 days and you can stay in PRC for 60 days or 90 days at most with the L type. Since you are now applying for it from a third country, it's hard to get a long stay duration. I agree with the embassy and it seems that you will probably get only 1-month stay duration. Anyway, if you want to stay longer, you can extend your L type seven days before it expires when you are at PRC. The documents needed are your passport, a registration form of temporary accommodation which can be obtained at the local police station, and a passport style photo, an application form, and your travel plan. It costs about CNY 168 to extend the L type, almost the same as you apply for a single-entry permit.