Yeah, that's simply a certificate containing a ECDSA public key, signed by the RSA intermediate "R3".
If you want your ECDSA certificates signed by the ECDSA intermediate E1, you need to sign up for the opt-in allow-list mentioned here: ECDSA availability in production environment
In practice, it doesn't really matter if your chain is ECDSA only or a combination of ECDSA and RSA. Only with HUGE amount of connections, the size of the certificate (due to the size of the public key and signature) matters.