Denisovan and Neanderthal vcf files

Question

[spiral01]

I am looking at Denisovan variation data obtained from http://www.eva.mpg.de/denisova/index.html. The majority of variants in these vcf files have a minor allele frequency of 0 (AC=0, AN=2).

As these variants are mapped against human variation data, does this mean a variant with an allele frequency of 0 is a polymorphism private to humans?

I am a little confused as there isn't much information on how these vcf files were constructed.