it's different from bisexuality where there is a certainty of being attracted to both male and female, whereas with ambiguous sexuality, there's no certainity, probably not even at all, and you're only sure of just how you feel when you develop a close and intimate relationship with someone who just... "clicks" with you.
Asexuals, the know they attracted to neither gender. Heterosexuals know they are attracted to the opposite gender. Homosexuals know they are attracted to the same gender. Bisexuals know they are attracted to either gender.
Sexually ambiguous on the other hand, don't have that. As knight_mage_rogue put very well: with ambiguous sexuality, there's no certainity, probably not even at all, and you're only sure of just how you feel when you develop a close and intimate relationship with someone who just... "clicks" with you.
I know asexuals that are attracted to people though. They don't consider themselves aromantic (I see you've acknowledged this already).
Is yours analogous to demisexual? I mean, I identify as a heterosexual, but there's no certainty that I'll be romantically or sexually attracted to any particular woman. But demisexuals can still identify as demi-heterosexual if they choose to, for example, so I'm still not sure if it's the same thing and hence my requests for clarification
Most of my learning has come from places like AVENwiki which doesn't cover a sexual ambiguous trait, which could be an omission on their part, but it's the principal reason why I struggle to understand because it's the first I've seen someone describe their sexual orientation as sexually ambiguous.