Anybody who spends any time making seeds has a huge pile of things that didn’t make the cut, or got mishandled and get chucked in the mystery bin. I think that’s probably what they are.
From the seed makers’ perspective, they’re great to give away, because they can’t really be sold anyway. Plus, it’s kind of fun just to pop some beans and see what you get. My guess is that they are all different, and even riot doesn’t know what they are – or only broadly knows what might be in there.