You're not missing anything. I clenched my teeth when I red this phrase. It doesn't mean anything and discredits the whole article as it shows the author has got a superficial knowledge in cryptography.
After all, unless you audit all the code fetched each time you load the page, they can mess with the code client side at any moment without anybody noticing. Is this not more telling about the limits of webdev rather than the skills of Mega's coders?
I haven't studied what Mega is doing at all, nor am I ever planning to; my point is just that however badly written the article is, there is indeed evidence that there's bad crypto in this system.
AFAIK this applies to any software.