M. A, a non-EU tourist, takes a flight from a small airport in the Schengen Area to the UK (non-Schengen). After going through securiy, they find the passport control booth closed and the door to the non-Schengen gates wide open.
Which they, along with all the other passengers, cross into the non-Schengen part of the airport unimpeded
Are there any precautions that M. A should take to prevent issues on further Schengen Area visit?
this is from a real life situation, though M. A in the real case is a EU citizen