Elliptic Curve vs RSA key length comparison
The comparison can be made according to know attacks and their timings. Your source doesn't provide a reference and date backs to 2015, so that is not a good site as keylength.com. The current values of this answer is taken for 2019.

ECC

For ECC 128 bit security means we need 256-bit curves due to the generic discrete log attacks that have $\mathcal{O}(\sqrt{n})$-time. Your cited page also matches this.

RSA

For RSA it is more complicated since there are different methods around. For example, NIST gives 112-bit for RSA-2048.

There is a good cost estimate with Batch NFS for RSA-2048 in area-time cost per key of about $2^{103}$ taking $o(1)$ as zero, rather than the cost $2^{112}$ advertised by keylength.com, NIST, etc.

Commercial National Security Algorithm, Information Assurance Directorate at the NSA IAD-NSA give 256-bit security for RSA-3072 and ECC with 384 bit.