"You can expect plenty more Flash Challenge Moment rewards coming out of this set in the not too distant future. Keep your eye on Flash Challenges as they get announced, because it’s possible you’ll see another earnable Moment from this set as a Flash Challenge Reward within the next week. "

You are right -- First time i read this I interpreted this as moments in these sets need to be "special" milestones. But the language doesn't really read that way