The way I read it, not so much “lower bit rate than the other disc”, but rather “the bit rate dips in the areas where the video gets especially problematic. Oh and by the way, those dips don’t occur on the 1080p disc”
Certainly a relevant point and not as reductionist as you make it sound.
I really don't want to belabor this argument, but this is what was written:
"[F]or every problem spot I double-checked, the 1080p disc easily outpaces the 4K disc. When the train pulls into Stoddard, the 4K discs leaves the impressive 70-ish mbps range of the credits and craters into the low 20s. The 1080p disc? Stays at a healthy 30mbps even peaking into the mid-upper 40s!"
To me, what he's saying there is: "30 and 40 are bigger numbers than 20. Therefore, the Blu-ray is better than the UHD."
Now, to your point, the next sentence is: "Obviously that number fluctuates but it stays relatively consistent without the dramatic flips from one scene to the next."
Even so, he's still comparing two completely different compression formats and drawing conclusions just by looking at the numbers. That's not how these formats work.
Again, I'm not arguing that this disc was encoded optimally. However, it seems clear to me that the real damage was done during the digital manipulation before anything got as far as the compression stage. The grain and detail don't go away because the compression bit rate is too low. The bit rate drops because the grain and detail were already removed during the "restoration" and there's less data to compress.