Yes it is -- its blockchain is longer. The blockchain with the longest proof-of-work is always the real blockchain, when given multiple competing blockchains to select from.
This is the essence of the Nakamoto Consensus Algorithm, which underpins the entirety of blockchain economics.
there are forks of bitcoin, to be sure... but the majority of "cryptos" out there are GPU mineable coins, because there's hardware that can be exploited to mine "profitably". not to mention the need to pre-mine shitcoins so they can be given to grifters and shills who pump & dump.
This is the essence of the Nakamoto Consensus Algorithm, which underpins the entirety of blockchain economics.