Not only, as Nab pointed out, the definition you linked inclusive of "aversion to" and "discrimination against", but if you want to get into semamtics about word meaning based on etymology, "homophobia" shouldn't translate to anything about homosexuality. The prefix "homo" means "same", so "homophobia" should translate to "irrational fear of the same".
It doesn't mean that because the word is relatively new to the language and uses the root words loosely. So, just because the literal word means "irrational fear of the same" that's not actually what it is defined as. Wherein, it can be inferred that since "homo" is applied loosely, so may be "phobia".