Maybe we need to start a thread for those of us interested in rules so that KFP doesn't yell at me for messing up his thread again.
With respect to the blurb you've quoted, it makes two points: (1) You don't need to touch the runner down, it's enough to touch the ball while it's touching the runner. That's the converse of the Malcolm Mitchell play I was taking about, and really not helpful here. Lewis was touching way more of Jack than just the ball. (2) The second point is that one that matters -- that a player can be down by contact before he has possession.
I've seen others on various places invoke the same principle that you and others in this thread have -- that so long as the contact occurs while the player is trying to gain possession it continues until he does. There are many on reddit saying it, and blogs everywhere are defending the call by invoking that principle. So far, though, I haven't seen anyone who can find a rulebook reference. The "guy writes books" argument is a good one -- and one that I'm prepared to accept, but it seems like there ought to be a rule somewhere. Because if there's not, then I am skeptical that it is correct for two reasons: (1) Despite the arguments some have made here (you could intentionally bobble, etc.) it seems very counterintuitive that you can tackle or down a player before he has possession. And (2) the one rule that does seem to clearly exist on down by contact (7(2)(1)(A)) refers to being down by contact as "runner," which Jack was not.
My suspicion is that your blog guy is looking at or discussing 7(2)(1)(f), which says it is a dead ball if the ball is taken from a runner on the ground. That's just not this play. That's a case where you have a runner who is not down by contact but who is on the ground, and you take the ball from him without otherwise downing him (touching him). Lewis was not a runner on the ground. If he was on the ground and still a runner, then it was not a fumble, by definition.
In short, if there is an interpretation of the rule that says a non-runner can be downed by contact by being contacted before he becomes a runner, it is not in a part of the rulebook that I can find. Doesn't mean it doesn't exist, but it would be good to have a rule reference.