AppleScript can interface with iMessage, so it's certainly possible to magic up an interface.

The screenshots I see just show a regular text message conversation.

Blue bubbles are for iMessage, green is for SMS.

It also says "iMessage" at the top of the conversation.

Good point. I didn't notice this distinction (I'm not current an iOS user). Although they claim you're communicating with humans, so they could potentially just be using iMessage at their current scale. Or the screenshots could be from a simple fully manual demo.