You were just lucky that there was nobody there to turn you away politely and point you to the "domestic" lounge

I have usually seen the desks manned, sometimes just one but often both desks - and never been able just to walk in. My experience is that I am fairly regularly in both lounges (- say weekly).

With that I am going to say that I have never seen the domestic lounge unmanned. So you never know with your luck!!