I think there was no problem with anyone drinking. It sounds like it was all done in a responsible way.
When it comes to teachers, my opinion has to do if the teachers were working. Where I live the teachers do not get paid to go to the evening activities. If they are there it is because they are volunteers. As long as the teacher was not tipsy I see no problem for them to have a drink with dinner before they attend an unpaid, non required, voluntary event.
I have actually been a parent in a similar situation. The parent who was concerned about us other parents having a glass of wine told us her concern while we ate. It turned into a interesting discussion about how alcohal effects people in relation to the amount of alcohal, empty vs full stomach, time after drinking, type of alcohal, etc. After the discussion and as we were walking accross the street to the meeting the parent said she still thinks we are all inappropriate.
We smiled, changed the subject, and she was never invited to dinner with us before meetings again.