A straight person told you they have same sex fantasies vs a gay person told you they have opposite sex fantasies? It seems that people are generally more accepting of the second case
Both of these situations are the same. People are people, wanting to experience something different, other than "normal", is understandable.
Humans are naturally curious and I certainly wouldn't make assumptions that either person is having a crisis of sexuality just because they are having same sex/opposite sex fantasises. Although fantasies can be revealing they have to be considered as part of an overall picture. Many of the people who write about same sex fantasies on this forum are in a much deeper cycle of questioning, where the fantasies have greater significance and relevance.