I have also had similar experience cold-emailing domain authorities. I spent days writing 10s of words, double checking my facts, doing my homework and have gotten a response everytime. They are excited that someone is reading their work, thinking about it and then having the gumption to contact them. I think it is actually quite rare.
I contacted a guy about a paper he'd written on image de-blurring. Just some high level questions because the paper was behind a paywall. He asked for my snail-mail address and sent a full color printout of the paper in a large envelope! I still have it.
