This has happened to me few times.
I had a ml who isn't the owner but acted as mamasan and if it's too busy and the door bell rings she would get dressed to head out and let tell the customers to come back later.

However there was this time I booked for ml however it was double booked or something cause when I came there she was working on someone else and it would take long. So She got me into the waiting room and asked do I want extras? I replied yes and she offered me a bbbj at the waiting room while her customer is already in the room. What was funny another ml came out to see what's going on and saw me getting a bbbj out in the open and yelled out "wtf!" Then went away.
I didn't last long and cim.

Another time I was with ml and similar to OP. She was giving me a massage then bbbj when another customer arrived with booking. So another ml comes into my room while I was laying on the bed getting bbbj and she starts talking in Chinese. I wasn't sure what's going on but I just laid there while the bbbj ml mumbled and shoo the ml intruder out. I didn't come, she stops and told me she'll be back. But in the mean time she gets the other ml to come in and gives me a massage instead
Strangest moment I experienced but I guess to them it's normal.