Does anorexia lead to smaller penis size?

No. The penis is the size it is. Plain and simple. If you had some fat around the penis and you were anorectic, then you could lose that fat and have a bit of a smaller penis but in general, the size penis you have is the size you will keep.
Not likely. The size of the penis is determined genetically. There is no fat or significantly large muscle in penal tissue so poor nutrition won't affect its growth - only hormones and genetics will. Theoretically severe malnutrition (significant starvation) can affect the body as a whole including it's many organs.