Taher Elgamal is also considered the "father of SSL", yet many later inventions that used SSL obviously weren't his.  Adam Back invented hashcash, but that does not mean that no person could have used this knowledge to create something new.  Also, Adam used a different version of hashcash than Satoshi, difficulty in hashcash was expressed in 20 bits.

You can also look on code written by Satoshi and Adam, and see they're not written by the same person.