He's dismissing it by saying people who can't come up with $400 in cash, can put it on their credit cards or borrow it from friends or family. That's pretty dismissive because the issue is that most people doing even reasonably well should really should be able to pay an emergency $400 bill in cash.
Except for the fact that the sort of person who cannot come up with USD 400 in cash is also the sort of person who has a poor credit rating and no credit cards, and most likely their peer group of friends and family are in exactly the same situation. This is the same sort of tone deaf advice that rich people give about starting your own company - "Why can't these poor people just borrow a few hundred thousand dollars from the family trust fund like I did, they must just be shiftless and lazy" - and should be dismissed in the same way. I suspect the author has neither been short of money in their life, nor met anyone else who was...
Not to mention the fact that a $400 dollar emergency is on the low end. In my experience, most emergencies that have cropped up have been closer to the $700-800 price (Doctor bills (after negotiation), vet bills, temporary relocation, etc).
