I'm a bit of an "asexual" myself, although I've never adopted the self-identification (I don't really see the need to categorize myself, I simply am what I am). I have never had strong, or perhaps any, physical attraction to either gender. I've been in positions where others have been attracted to me, yet rarely have I reciprocated (the odd time that I have, it was never serious in retrospect).
Neither do I have any desire to have sex. I can live happily without sexual activity of any kind, whether actual or masturbation.
Nevertheless, since we are both human, we are still
sexual beings on some level even if we don't experience much or any attraction to women or men, nor the desire to be with them sexually, and so it should not be surprising that when we are aroused or "intrigued"
drool
that we have fetishes and wants like everyone else. You don't need to experience physical attraction to others to enjoy sexual fantasy.
In your case, its spanking. I don't think that this affects in any way your identity as asexual.
Some asexual people are very sexually active. They have romantic feelings for people of other or their own gender, and on that emotional basis have sex even where physical attraction is lacking.
Within such a broad orientation, there is a great deal of wiggle room I think for someone to call themselves "asexual" in their own way.
