They don't claim to have invented CDC, or FastCDC, they just made and are sharing a useful implementation of it.
And if that Tarsnap presentation is from 2013, and FastCDC was published in 2016 [1] according to Wikipedia [2], then presumably Tarsnap didn't invent FastCDC either.
Another well-cited predecessor is "A low-bandwidth network file system." (https://dl.acm.org/doi/abs/10.1145/502034.502052), which was published in 2001. It uses Rabin fingerprinting to define chunk boundaries.
