Is a man sitting with a woman in a public place—such as a waiting room—that people can enter at any moment considered a private seclusion (khalwa)?

Unlawful khalwa (definition) (private meeting) is the gathering of a man and a woman in a way that does not ensure the absence of suspicion. It requires the place to be hidden from sight and sound, and that the entry of a third party is unlikely. Waiting rooms and similar public places, where one cannot control who enters, are not considered unlawful khalwa. However, it is preferable to avoid sitting in them alone, due to the whisperings of Satan that such a situation might lead to.