Yes, and the renderer is the same as in Cinema 4D which is used by many, while custom ray tracer build for Geekbench is not used outside benchmarking.

The blog post you linked just shows that one synthetic benchmark correlates with another synthetic benchmark. Where do SPEC CPU2006/2017 benchmarks guarantee or specify correlation with real-world performance workloads?

Cinebench fits characteristics of a good benchmark defined by SPEC [1]. It's not a general benchmark, but biased benchmark. It's floating-point intensive. It should do a perfect job of evaluating Cinema 4D rendering performance, a good job as proxy for other floating-point heavy workloads, but a poor job as proxy for other non-floating-point heavy workloads. The thing is, most real world workloads are biased. So, no single-score benchmark result can do an outstanding job of predicting CPU performance for everyone (which is what a general CPU benchmark with a single final score aims to do). They are useful, but limited in their prediction abilities.

[1] https://www.spec.org/cpu2017/Docs/overview.html#Q2