The (7,4) Hamming code means four bits are put into the encoder and seven coded bits are returned. And since there are four bits in, there are 16 (2^4) possible codewords.

THE HAMMING(2072, 2048) ENCODER The Hamming(2072, 2048) coder divides the input data stream into 256-byte blocks and computes 24 bits of parity that are used to correct all single-bit errors ...

The (7,4) Hamming code means four bits are put into the encoder and seven coded bits are returned. And since there are four bits in, there are 16 (2^4) possible codewords.