It depends who you ask.
IMO the terminology surrounding all this is not yet fully agreed upon and/or understood by many and frequently misused. The clearest example being the way the word gender is thrown around to mean both biological sex and gender expression aaand gender identity.
If we're talking non-binary in terms of biological sex, then I don't know what to make of that. Doesn't make sense to me. Plus there are technically at least 3 sexes because of intersex. So it's not binary to begin with.
If we're talking non-binary in terms of gender expression, then that seems perfectly normal to me (from my interpretation). Although it is again an umbrella term with a bunch of sub categories, some of which conceptually contradict/disagree with each other.
So, it's complicated.
Broadly speaking though, non-binary generally means people who don't identify entirely with one of the traditional gender identities of male or female and the gender expressions that are associated with them. Sexual preference is a separate matter.
Yeah, complicated.
If you want to swat up on this stuff here's the rabbit hole.
http://gender.wikia.com/wiki/Gender
Initially I found wrapping my head around all the terminology can feel like trying to find the end of a piece of string while swimming in spaghetti.