No SERO is not exactly a hardfork of any other blockchain, the SERO team has only sourced few bits of ETH code that makes it possible for SERO to work on Hybrid transaction model that supports both UTXO + ACCOUNT models of transactions.
SERO primarily means SUPER ZERO, "Zero" coming from the privacy cryptographic protocol - Zero Knowledge Proof and "SUPER" is inspired from the "SUPER-ZK" library that is created by SERO team which helped us achieve approximately 20 times faster encryption against Zcash doing testnet.