I'm reading a BBC article on ketamine abuse. In the article it says:
The doors at the Baiyun drug rehabilitation clinic are always locked, betraying the fact that the patients inside aren't always there by choice.
It doesn't make sense to me that locked doors at a clinic betray the fact the patients aren't there by choice. I am from the United States and I know it's possible the United Kingdom may have some alternate meaning I'm not aware of. Or maybe I just don't understand the word's application here? Thanks