Considering the amount of alien-related stories in entertainment, I wouldn't be surprised if the teacher concocted the homework based on items kids
would be able to easily relate to. If that's the case, it obviously worked if your daughter is still talking of it.
The teacher's use of aliens, may be a result of the trend. The trend in the media, however, might be part of a kind of disclosure.
You said that the teacher told the kids aliens were coming to pick something up, and were here to help us might have been said to avoid scaring the
children, since many many cartoons depict aliens as being mean creatures (Justice League sagas, Godzilla sagas, etc.).
However, I can't think of a good reason why the teacher would go into such detail about the landing locations and what not, but that's a description
we've heard of over and over... I mean, even in Halo, the aliens land in Africa. Although in Halo, even though the aliens think they are there for
the better of the universe, they are still out to get us!