You should really watch it if you're interested because it doesn't have a simple summary. However, I think the core idea is that games are art and they can be used to convey strong emotion just like other forms of art. They don't have to be about fun, they can be about the experience like paintings, books, or movies don't always have to be comedies.
I had it running in the background so take this summary with a grain of salt as I only heard half, but the catalyst is that her daughter comes home from school, they’ve had “Black American History Month” or something like that, and her daughter gives a recap of what she’s learned.
She then wants to play a game and her mother gives her some bricks shaped like people and ask the daughter to group them as families — after some time the mother then introduce the rules, which are loosely modeled on slave transportation — after a while the daughter realize the horror of it, asks if that really happened, etc.
This is just within the first 10 minutes or so of the talk, the speaker then goes on to tell how this inspired her to create other games, with Train being about the holocaust — it is a pretty emotional ride listening to how people reacted to and played this game.
Part of the Flash presentation was broken for me. I got to the section about "the handoff" and the slides turned into a big green rectangle. Fortunately it came back after it moved on to the next section.