This is not surprising. The extreme distaste those born after about 1971 have for Trump was evident in the GOP primaries as well.
As many over 45 will no longer be voting in 2020, I believe this gives Trump reason to worry, even if, as some reports suggest, the next wave of new voters is a bit more "conservative" than the last.
Gen Z is probably gonna be the anti-thesis to millennial. Generation 9/11 grew up on patriotism, support the troops, and war video games like CoD. If anything I expect more of a social libertarian streak but they will not be liberal or more so than millennials on economics and domestic issues. The universe must remain in balance so generation 9/11 must cancel out the SJWs
Practically no portion of GZ is even eligible to vote yet (none are by some measurements). The generation you're describing as "9/11" are Millennials, and with particular note, the events you described occurred concurrently along the politically-formative years of the segment of Millennials who are the most Democratic as a whole (those between 25-30 years old).
The reasons you list for why they'd be Republicans are many of the reasons why they're Democrats in the first place.
Aren't there some polls that suggest younger Millenials are a bit more Republican than older ones? Or maybe it was just younger White Millenials? Ancedotally, that is what I have noticed - the people I know who are 26, 27 and 28 tend to be more Democratic than those who are 23, 24 and 25.
Yes, the younger cohorts among Millennials do appear to be a bit more conservative than their older peers; somewhere in the vicinity of 50/50. That's the byproduct of coming of age under a two-term Democratic President who was polarizing in the national dialogue (even though I'd wager a clear majority of them actually like Obama). Trump may dull the effect a bit and cut off potential gains among GZ.
Basically wherever you are between 16-20 has the biggest impact. Try being 15 when the Iraq War kicked off, 16 when Bush got re-elected, 17-18 during "the surge" and 20 during the economic collapse/rise of Obama like me. 
Maybe he's being more broad, but what he described (9/11, "grew up on patriotism/'support the troops'", Call of Duty, etc) is the climate that people my age came of age in (2001-2008) and we're the most Democratic of all Millennials - other than CoD games still being around, I don't think it's a climate that applies to teenagers today.
This wasn't the case with my peers. I'm 21 and most of my friends are 20 so we're definitely the younger half. We vaguely remember Bush leaving office and everything was bad and that Obama was an improvement over "everything being bad" Bush.
But I guess I can see us being slightly less liberal than those who saw full force all of Bush's screw ups. Likewise I suspect those born 1999-2002 will also be quite liberal given what they're gonna witness growing up under the Trump and Pence administrations.
Gen Zers are generally too young to remember anything about Bush, especially in the more restrictive definitions (i.e. the ones that start at 2000 or 2001).
