I'm a grown up.
I work in a professional environment.
Nipples happen.
there, I said it.
Nipples happen, boners happen, nice asses "happen".
Complaints like this are 90% women, 10% religious men. Usually made by people who are easily drawn away from their actual work into bullshit topics like "what other people are wearing" or whatever fucking rumor is floating around.
In other words, the top complainers are those who act unprofessionally to begin with.
If a women is attractive, she will draw eyes no matter what. If she has a nice ass she will draw eyes. It works both ways with guys.
Its human fucking nature.
We've had plenty of occasions where the "hot girls" have come in and nipples happened or the pants that they were wearing highlight an ass so perfect (takes a moment to reminisce some fappable asses).
You take a mental snapshot, plan your movements in the office to coincide with viewing opportunities and then you GO BACK TO WORK.
Unfortunately in our litigious society, companies have to cover their asses to protect against anything that might anyone "uncomfortable".
The women who received the warning hopefully will be able to identify the person who complained. My recommendation to her would to file a complaint that the complainer is making her feel uncomfortable by constantly staring at her breasts.