That clearly was not a fumble, it was an awkward pump fake followed by two steps
This tweet basically admits the refs got it wrong:
Fumble = legal, and no travel. No fumble = travel. It's understandable for people to think that the offensive player doesn't lose control, and therefore travels. But the officials on the floor deemed it a fumble, and therefore legal. This is what makes this job so difficult. pic.twitter.com/81igLXM9MG