why was there not a lot of applause when he started talking about RUN --mount??

I'm a fairly confident Docker user. The first part about buildkit was very nice, clear and very useful. I had no idea what the second part of this talk was about. Why is this man talking about "frontends" (huh? web, mobile, what is going on?). And why are we suddenly talking about some API in golang? Is this even remotely related to Docker? None of this was explained and it took me a while to grok what was happening. At that point, I got back into it and overall this was a very informative video.

Can secrets be accessed using non root user, not all docker images are created using root user and not all URLs are downloaded with root user?