Hard drive showing up as 120 GB SSD when it is 1TB fusion

I recently sold my old Mac on eBay and was contacted to say that it was falsely advertised as a 1 TB fusion drive, when it only has 120 GB SSD. I was horrified I may have made a mistake (it's a Late 2014 model so I had no memory of what it was when I purchased it), and the woman was so awful I just issued her a full refund and let her keep the computer. However I just found the purchase invoice and it clearly says "iMAC 27" 3.5 GHz i5/ 2x4GB/ 1TB Fusion/ Retina display". However under the Apple - About this Mac - Storage it does actually say 120 GB SSD. She says I must have changed it, but I didn't. How could this possibly happen?