The lesson states:
To express to need + [noun], you will use :avoir besoin de/d' + (article) + noun
The examples cited show the use of the indefinite article but none include the definite article and it could be implied that the definite article is never used after avoir besoin de/d' which is obviously wrong. It is the old problem of the specific vs the general. Since this is a perrenial problem for French learners, it might be an idea to spell it out more explictly in the lesson.