"That was our thinking when we first started working on human.io."
I think it's important to have that first, otherwise you are burying the lead. Although I can see why you wouldn't want to prematurely niche yourself, I don't think the pitch about engaging your users is especially compelling.
"what would it mean to invoke methods on a person?"
I mean ultimately you want to be selling the benefits and not the features, so I think being able to communicate the implications of that statement are much more important than being able to come up with a snappy analogy for the statement itself.
If you're really committed to staying neutral on usage though, we already have the term HCI for human-computer interaction. So maybe you could describe it as an HCI programming language or something.
That was our thinking when we first started working on human.io. If GMaps lets you invoke methods on a map, and Twilio on a phone, what would it mean to invoke methods on a person?