Totally agree about Facebook messenger. This is a game changer. FB messenger is going to be the I'm-on-the-subway-and-don't-know-anyone-so-I-better-not-look-silly kinda app, and that's boring.
It means people will user Facebook messenger when they are not comfortable with the place they are in.
If I'm at home, at my university or my cousins' I will chose Snapchat over Facebook messenger, because I'll feel free enough that I can talk and goof around with that app, in a way that is not possible with Facebook... yet!
Also, I think there are people less boring than me who will not give a damn and will use Snapchat's Chat everyday, everywhere, and that's going to be awesome. As clichéd as it might sound, they really are changing the way we communicate.
I think he's referring to lot of people that spend their time mindlessly sifting through their smartphone in order to avoid eye contact with a stranger.
I think the fact that it's in Snapchat combined with the disappearing messages will yield different use than FB messages. I think it'll be used for when I'm bored and feel like sending silly messages, rather than serious conversations.
It also seems like a full on attack against Facebook messenger.