Do you mean the "Formally, it is a quotient object in the category of (small) categories, analogous to a quotient group or quotient space, but in the categorical setting." sentence?
Doesn't a path equivalence relation on Free(G) exactly the congruence R they talk about on the Wikipedia page? Can't we define the quotient category Free(G)/~ in very much the same way, such that there's a quotient functor Q which equates certain paths?