Yup. All the technology required to make it work is quite old. Just need the time and money to tie it all together.
Books already carry an ISBN to identify them, and ePub supports setting unique IDs in the metadata, including an ISBN. But for at least 20 years, it's been possible to 'hash' a computer file into a short string that would turn out different if even one bit changed in the file. Compute the hash, and you have a unique ID for that file. That hash can then be used to confirm that the file hasn't changed, or that file A and file B are identical or not.
I can't say if Sony actually did this, or which unique ID they use: the one in the ePub, or the computed hash. I'll probably know a bit more once I have my T1.