A potato queen is a gay asian male who is predominantly attracted to only gay white males. 'Potato' describes the gay white male AND his supposed primary food form. Queen describes a gay person of flamboyant nature.
This exclusivity in affection for the 'other' race is often ridiculed by other asians and deemed as betrayal or abandonement of one's own race/culture. More often that not, a potato queen is labelled so by others, not a self claim.
The 'potato queen' along with its family terms such as 'sticky rice' and 'rice queen' in itself is frowned upon today because they're viewed as stereotypes, in a gay world that has far too many already.
Cho is a potato queen because he is only sexually attracted to caucasian men.