My evidence for this assumption is that the "pet" appears to be able to fit into the "hole" in the Warlock's gauntlet perfectly, plus it has a rather identical appearance to the Traveler. If I'm right I think it would be a way for the Warlock to have a cool down for his abilities,after every use the "pet" would pop back out to recharge. When you are ready to use it you could then summon it from your side back to the gauntlet.