Length of ElGamal signature compared to RSA signature
Mistakes happen.

The author's scheme adds a signature about twice as large as $p$, when RSA signature (of the textbook variety of the reference) adds a signature about as large as $n$. It is clearly assumed that the public prime modulus $p$ is about the size of the RSA public composite moduli $n$.It follows that the size of the signature in the proposed scheme is twice that in RSA.