F*** Box Office Mojo. Those snide comments don't really have any basis, really. Those are really just the opinions of the person who wrote that. Unless they polled people and asked them if they do or don't know what the movie is about, it sounds like the writer hasn't been paying much attention to the movie and knows nothing about the story or the character.
Also, I really don't think Green Hornet will affect this movie's box office results at all. Aside from the color green and the fact that both characters where masks, they have almost no similarities (at least not Seth Rogen's crap version of GH). I don't think anyone is going to get them confused other than people who wouldn't go see a superhero film in the first place.