No, a drawing in a manuscript is not a reliable source because those who commissioned manuscripts wanted a "perfect" depiction of the world. Everyone appeared much better dressed than they did on a daily basis.
Which of these reasons did you include in your answer? Check all that apply.
A. No, a manuscript illustration is not a reliable source.
B. People are too well-dressed.
C. Patrons wanted a romantic view of the “perfect” world.