I think I know what's up with this one... The fact that you could tell she was Vietnamese from your first conversation means that it must have been pretty obvious she was a foreigner.
Now human psychology may be a universal thing, but it's been posted here before that the specific PU routines developed in this community are most effective on women of European descent. Just look at posts made by people who visited, for example, Japan. The problem is that it's easy for subtle, indirect game to be interpreted as friendliness, and if you suggest meeting again, they'll likely agree out of politeness.
If this kind of thing is a concern for you, just focus on building attraction more before you get your hopes up about a number. Look for universal indicators of interest such as body language if they aren't native English speakers. And even if you did build up a lot of attraction, her bringing the boyfriend is still VERY unlikely and could be due to factors outside your control. For example, maybe she was planning to go out in secret but he found out and demanded to come along.
