Peter King of SI.com called it the "worst interference call of the year."
It came on a 2nd and 10 from Houston's own 45 with 1:54 left in the game. The Texans were driving to at the least tie the game on a field goal or at most win the game with a touchdown. QB Matt Schaub dropped back to pass and found WR Andre Johnson 31 yards down the field near the sidelines.
The video (which you can view here) appeared to show that, if there was any penalty, it was Johnson pushing off of Flowers (then again, I'm pretty biased). Johnson after the game explained the play from his viewpoint.
"During a lot of our routes today, they were bumping us while we were down the field. In that play, I did a go route and I knew (QB) Matt (Schaub) told me if I had a single safety that he was going to give me a chance. He told me that earlier in the game. I was just determined that they were not going to bump me around. He tried to run into me and bump me and I hit him with a little elbow to create some separation and was able to make a play."
I saw Flowers' hand go up slightly and make contact with Johnson early in the route but when the flag came down what you saw was Johnson elbowing Flowers.
You can't do anything about it now but that's a frustrating call with which Flowers clearly disagreed.