It is during the dry season but from my experience most resorts will consider peak season to be from mid/late December (holidays) through March. Doesn't mean that you can't have dry weather before and after that, you most likely will but April is already when the peak season is usually tapering off and that's why you may have been offered better upgrade pricing. Again, this is just my theory and once the OP let's us when they got the higher pricing for, we'll know if it holds any water or not.