I really doubt that there's anything you could have said that would have had any impact on these guys. One of the guys was perpetually smirking whenever anything related to blockchain technology outside of bitcoin was discussed. I've run into this kind of this mentality before (more in religious areas than in technical areas, ofc) and generally any reasoned argument you try to make will just be ignored or derided.

I'm not saying it's impossible to change someone with this kind of attitude, but it's pretty much impossible to do it in one session, and it's usually going to take arguments from a lot of people they know, since they don't generally have the technical abilities to understand the underlying issues and have to rely on the statements of authorities they trust. Don't get me wrong, I'm not saying this is totally crazy: I don't bother to educate myself in every area of study either and I rely on other people's opinions to some extent in lots of things. But I try to keep in mind when I'm doing that, and keep an objective view when I hear opposition to such opinions (as you suggested at the end there).