It's hugely important! How would you feel if some one came up to you and said you were cute but looked like the opposite sex. Also don't answer that as I know most of you will roll with it.
Within the context of the show,(with their images they are posting) i think it's supposed to be seen as something mildly innocent, seeing as it's one of very few modern anime with main characters who are gay/transgender, and Very openly so too.
Korra and Steven Universe spoilers??
In the context of cartoons, Korra was only really brought to light on directors Tumblr, and in Steven Universe they are gender neutral characters. And the directors strongly reinforce this.
But answering the question;
In reality, i guess it would really be depend on who this was and whom they were reacting too. Some people would see it as quite innocent. But context dependent ;D