Before Jack went up to ambush Goliath and The Real Man, he had cast the Body Double. During the entire endeavor, he had controlled his doppelganger to run toward the capital. The copy created from his Body Double skill could last five minutes, hence he had been keeping a tab on the time. He let go of The Real Man when it was ten seconds left before his skill expired.
Unfortunately, his hostage could not let go of his grudge and decided to kill him, so Jack took him out. When Goliath charged at Jack, Jack finally switched places with his copy at the last second before the skill expired. The skill ended once he traded place with his copy.
He reappeared at the place where his doppelganger was a moment before. He looked at his surroundings and checked his map, he was actually ahead of Bowler and the others, so he decided to stay at his place and wait for them.