There is a big difference between competence in a field and encyclopedic knowledge.
“Competence in the field” is everything related to the concrete information related to the technical aspects of a field. Technical texts require a technical fluency based on the mastery of a specific area of knowledge and its lexical and terminological aspects.
Encyclopedic knowledge is the result of pieces of cultural information of a more general character. These pieces are references to cultural baggage that is shared by a certain community that normally appear in encyclopedic works and not in dictionaries.
All intertextual references are important, meaning allusions to older texts, historical references, or a diverse heritage of cultural knowledge.
Being in a rush and relying on the brief consultation with a bilingual dictionary or simply not knowing encyclopedic information can come together to cause errors on a large scale.
The text is not reduced to the format of the page and the interpretation of the result does not give way to a quick reading. The job of a translator is to deactivate that mine field of extratextual references. Newmark has correctly compared translation with an iceberg: the largest part is under the surface.