Great article - there's a song in Avenue Q which seems pretty apt here. It seems that Van G has presented the 'not all black people are racist so racism doesn't exist' argument, tried and tested by white folks the world over. You didn't say all black people were anti-asian, but were attacked as if you did.
Dennis has a much better argument, but one that is fatally flawed given that he puts white people at the top of the pyramid and then people of all other skin colours underneath in equal weighting. I'm not sure how this plays out in the following example. An asian family living in a predominantly black neighbourhood, an asian man making sexual advances to a young black woman.
Dennis notion of interpersonal power equating directly with skin colour in all situations is flawed and simplistic. It allows him to both be the victim and never the perpetrator. It allows black people to attack asians with hatred and malice because of their race and for this to be considered prejudice rather than a racism. In short, it will always be white people's fault and black people can be infantalised away from their responsibilties as citizens and individuals. It's a form of pernicious groupthink and you did well to stand your ground.
For what it's worth, I don't think it's encumbant on any individual to apologise for what other members of their race have done. Why would you? You're better off focussing on your individual journey towards being more inclusive and empathetic, something I think you've done a far better job of than either of your commenters. Great article, very enjoyable.