It could be defined that way. But your set is in a way more difficult to resolve as it has only one element. In the diagram the number of elements (4 sets) of the set is equal to the number 4 i.e. a set defines a number by simply counting its elements.
There are probably some other nice properties if you define it that way.
*Most fungi... Others can. https://en.wikipedia.org/wiki/Mucormycosis