How do you know if you're playing with somebody who never played Journey before?

Observe them as they wander around. I take the following as signs that they're likely NOT a new player, but there's no surefire way to tell if they're definitely new, as was said already:
1) Patterns on the hem of their robe
2) White robes
3) Moving directly towards sigils (powerups), glyphs (murals), or key checkpoints
4) Starting to charge their burst up about a second before they arrive at the place they'll use it
5) Bursting again get a second, mid-air boost from the flocks of ribbons in order to get even higher
6) Shorter chirps and only for specific reasons

In my experience, the players I assume are new tend to wander around a bit more, have a tiny bit more trouble with game mechanics (particularly flying on early levels), hug you a bit more, and are more chatty with their chirps.