Thomas Gross' comment above is on target. Nouns and pronouns (and other linguistic categories) have both identity of sense and identity of reference. The default situation sees a pronoun adopting both types of identity from its antecedent, e.g.
A. Fredi likes hisi meal.
The definite pronoun his takes both types of identity (reference and sense) from its antecedent Fred. The traditional binding theory (Principles A, B, and C) from the 1980s was developed to address the distribution of pronouns (reflexive, reciprocal, and personal), whereby the theory was not generally distinguishing between these two types of identity.
Definite pronouns (e.g. he, she, it, etc.) have an identity of reference that they adopt from another entity in context, and the standard case is for them to also adopt identity of sense from the same entity. There are many cases, however, where there is divergence, i.e. the pronoun adopts the identity of reference of an antecedent (or postcedent), but it does not adopt the identity of sense of that antecedent, e.g.
B. Shei is my friendi.
C. My friendi is heri. (Pointing at someone across the room)
Example B violates principle C of the traditional binding theory, and example C violates principle B thereof. These violations are, in fact, not really violations because they involve a divergence of the two types of identity. In each sentence, the coindexed expressions have the same identity of reference, but they have distinct identities of sense.
The word one in English is the stereotypical example of a pronoun that takes only identity of sense from its antecedent (or postcedent), e.g.
D. Tom read a book, and Sam read one, too.
E. Tom read a book, and Sam read it, too.
Sentence D has the indefinite pronoun one adopting just the identity of sense from its antecedent a book (a book, but a different book), whereas sentence E has the definite pronoun it adopting both the identity of sense and the identity of reference from a book (the same book).
The example in the question illustrates this same divergence of the two types of identity:
F. Steven King is Richard Bachman.
The two names Steven King and Richard Bachman have the same referential identities, but distinct identities of sense. The traditional binding theory, when it is presented in a superficial manner, does not distinguish between these two types of identity. This is the source of the confusion expressed in the question.