I would expect that a person conscientious enough to know how shocks, wheel size, tyre type and pressure, saddle type, and speed affect ride comfort would also include that information in their post.
Therefore, these anecdotes amount to "I rode on two different bikes which happened to have different frame materials and I could tell a difference in the amount of vibration." Meaningless, even if we don't consider human biases, after all these aren't blind tests.
I would be curious to know if there is a difference that can be felt, but in the end it's of no practical use. I bet even slightly adjusting your tyre pressure will have 10x the impact of any possible difference in frame material.
I could have left out my anecdote because it is subjective and prone to bias and error, but it is how I believe I can rule out (some of) the commonly cited reasons of different bike feel -- seat posts, because that would not affect vibrations coming through the feet; and tire pressure, because different tire types and pressure have their own different and recognizable feel (e.g. responsive and jittery with high pressure, squishy and sluggish but not silky smooth with low pressure).
At the time, I assumed the difference was the frame material, but I really do not know the cause. I do believe there is something that could be quantified as opposed to just a psychological effect, but it could be something non-obvious like the typical curved shape of old steel forks; or the frame geometry or tube diameters; or even something else that just correlates with frame material like the tendency of old steel frames to have hand-built wheels with lots of spokes as opposed to the newer (seemingly) rigid factory wheels with fewer spokes.