American here, I honestly thought that fag was a synonym for asshole or jerk until I was like twenty. It's hard to say how many of my peers also didn't realize it was a slur. Obviously I don't use the word anymore.
Think its supposed to represent a cig after sex(or jerking it?) no clue if this screenshot is unaltered or not, all I know is that all gender expression is valid and that femboys do be hawt.
I definitely took it as meaning either they're nervous about being called out and so nervously taking a big drag on a cigarette or as others have pointed out as an after sex cigarette. They probably did mean "fag" but considering they're American then very few of their intended audience would assume that.