What did he call the theory? What was the speakers name?

There are many alternatives, but very few are fleshed out and most are just frameworks

It hasn’t been “proven” because it hasn’t been experimentally observed.

But most models treat it just as a subatomic particle that only interacts with gravity

I think you misheard what that guy said, because the leading theory is still 100% an unknown subatomic particle, and I would hazard to guess that 90-95% of physicists in a field involving dark matter believe that it is just that— matter that only interacts with gravity, or interacts extremely weakly with the other known interactions.

Most of the debates around dark matter are around the question of “what TYPE” of matter is it and there is really only one fleshed out alternative theory— MOND and it’s various offshoots— and it’s clunky and overly complex due to initial failures, and it still fails fully resolve the initial issues that led to the need for dark matter.

A universe filled with a cold subatomic particles that ONLY interact with gravity (not even itself) not only fixes most of the problems that required dark matter in the first place, but people are using it in other areas (universal structural evolution and such) and it works there, too.

Until dark matter is experimentally observed, it is still an open area of research…. But given decades of failures of alternative theories and cutting edge research discounting other theories, it’s getting harder to treat the cold WIMP theory as anything but accepted.