Why would seeing sexual imagery make you less rational? That doesn't make sense.

The study you mention say the people were already in an arousal state (that they had to induce themselves). It's very different from seeing images that you may simply ignore, evaluate differently, etc.

Also, there is the bias that if people are looking for such images (because they really want them), they are probably more willing to drop recommended practices, and hence make irrational moves. So irrationality doesn't come from seeing the images at the first place, but from their willingness to find / see such images.