we were done first and walked back in on them mid-play... what's the etiquette here

M44 / F42, ls couple about 3 yrs in, we usually do separate rooms with our two regular couples. last weekend at a friends place in seattle, separate rooms, we finished our round first. like a solid 25 minutes before them. we got cleaned up, got robes on, made some tea, sat in the kitchen. and then... we didnt really know what to do. eventually we just walked back into the playroom where they were still going. i thought it was fine. she thought it was fine. but afterwards F from the other couple mentioned she felt "watched" in a way that was different from same-room play because they hadnt signed up for an audience, we just showed up. i hadnt thought of it that way. we didnt sit and stare we kind of leaned in the doorway and watched a minute then sat on the side of the bed. but to her it was uninvited which is fair. so my actual question, what's the etiquette in separate room play when you're done first... do you stay out completely until they emerge, do you knock first, do you only come in if invited by them earlier in the night. how does your group handle this. is there a "you can rejoin when finished" understanding that we just never made explicit