Flash Sentry's appearance didn't bother me much. In EqG, he was just a plot convenience...The "pretty boy" for Twilight to fall in love with. Meghan McCarthy tweeted back in June that Flash Sentry would not be a character in Season 4. His cameo in Three's A Crowd was a little shout out to EqG and perhaps to confirm the movie was canon. I don't think Twilight is going to become his "girlfriend" or anything, he was simply a high school-esque crush she had.