I wouldn’t lock it, why would you? The design of 2 tables is obviously so 2 parents can use it at once because I don’t think twins accompanied by 2 parents is common enough to be the thought process. When you lock it’s just deliberately trying to inconvenience another mum. And privacy?! Wtf it’s another mum and baby! Have you never changed your baby somewhere where there isn’t a lockable baby change? Car boot, park bench, on the floor of the ladies when there isn’t a table… Will your baby go to nursery and be changed by nursery staff in front of other nursery staff and the other babies? What if they need a wee in the park when they’re potty training? Sorry but I just don’t get it and think it’s really strange! Ditto 2 adults to change a baby though, talk about unnecessary! And how would that be quicker? Babies are small, only one person can wipe at once. Again, I don’t get it. We just take turns, same as all the other parents we know.
I still wouldn’t have said anything to you though, too British, but I’d be very annoyed at needlessly having to wait.