It looks like AncestryDNA reported the reverse (minus) strand of the double helix for that particular SNP. The complementary bases on the double helix are A<->T and C<->G, so your alleles would be AA.

A few other SNPs with different strand orientations have been reported. Some of those could actually be because 23andMe or FTDNA reported the minus strand. Maybe at some point we'll get a consolidated list of those SNPs, but in the meantime, most 3rd party utilities allow a little bit of wiggle room for non-matching SNPs.