Don't be sad! First of all, even though they said they have no ranking for the alternative list, but I think the ranking is based on the order of interview time. Whoever got interviewed first would be first on the list. This makes sense, right?
Secondly, many students would choose other schools over Boston because of its tuition. Boston is a good school, no doubt, but it is expensive so many applicants would decline Boston's offers. I think Boston sends out a lot of acceptance letters to fill up its class, so do not worry too much!!!
Good luck!