I think the claim that the difference in the first pair was much bigger was probably overstated. Would I say the difference appeared bigger in that case? Yes.

I think the claim that the difference in the first pair was much bigger was probably overstated. Would I say the difference appeared bigger in that case? Yes. But on a calibrated screen, as someone with no known colour vision deficiencies, and as someone who does a lot of design work including fine-tuning colour schemes, there is a clear step between each adjacent pair of reds on that scale to me, and the perceived differences between the steps aren't that big. If I had to guess, I'd suggest that some people see the second red darker than it should be due to poor colour reproduction on their monitor, which would exaggerate the difference from second to third red.