Word did indeed reach Roy Mustang's office pretty quickly once the stranger was spotted, however the first person it reached was Riza Hawkeye. She didn't like strangers, in her experience they always meant trouble. So, while Roy was finishing up a meeting she decided to go and see for herself what was going on.
If she discovered this person was trouble or interesting she'd ask him to accompany her back to the office. She knew Roy wouldn't be happy but at the end of the day it was her job to protect him and she took her job very seriously. Informing the others where she was going she made sure Roy would be watched while she was gone and headed out to intercept the stranger.
He was easily spotted on the street, almost everybody was staring as he passed though he seemed undaunted by it. "Excuse me" she called out, "May I speak with you for a moment?"