Thanks everyone. This is actually my son's only American friend (DD has one other) and they are very much a part of the American community here--so I thought maybe things had chagned in the US while I wasn't looking

Even before we came here the kids hung out with a pretty small group the last 4 years or so and I truly wasn't sure if this would strike others as normal. I appreciate knowing I am not totally off base.
Honestly, I was just taken so by surprise. DD was in the car, the boy was getting his bike in our garage and the can was cranked, mom rolled down the window and yelled out to her son that he had to write the essay before he left for candy/golf and then looked at me and said--"I gave him an assignemt becuase of his behaviour this morning" (in the same way you might say "He has $5 on him to pay for hiw way" or someting) and just drove off.
I know she uses essay writing as a punishment with her kids normally so it was not a joke (this bugs the heck out of me because I was an English teacher and making essays into punishment just makes our job harder but that is another thread).
Anyway, it took him about an hour to write the essay and then we went off. Luckily the candy shop only had a 20 minute line--it is our first sunny day in nearly two weeks so I think everyone wanted to be outdoors. This friend had never been to the shop and loved it so that is good.
We just got back from mini golf. We only had time to play one of the two courses (both had been planned) but at least they mostly got their day and I have a better idea of how to handle it if it happens again (the being late because one or more kids had not doe a job is fairly common, though not normally this late--even to girl scout meetings she runs; but they truly are nice people most of the time--I like them and my kids get along great with their kids). So anyway, it was not a lost day and now I know I am not crazy either
If the mom kept the boy home, all 4 kids would have been punished because she would not have been able to take the girls swimming. I agree with you, the punishment should have been completed LATER or the even rescheduled.
She could have left her son home alone (does it often) OR I could have taken the girls and my son swimming. I honestly would not have minded if she cancelled all together (though it is not something I will do--I do not allow my kids to inconvenience others at the last minute due to their issue but I know that really works as a strong deterrent for some kids and i do not blame parents who do it that way) but I just felt put put being the bad guy and then not even having the possibility of doing something else fun with my kids while we waited.