http://healthyeating.sfgate.com/much-sugar-mango-7628.html
According to that link they (mangoes) have a lot of sucrose which, if I understand correctly, is plain ol' sugar.
So it's probably properly labeled. I don't think I've ever seen an ingredient list on a potato, whether or not it's in a bag. Chunking and freezing shouldn't change much except for perception. Freezing and thawing could cause a separation of the inherent elements that causes a different experience.
Of course, it could be totally fraudulent, but it would take a lot more to determine that.