That seemed like an ill-spoken line. What's happening here is that a row of dominoes is falling because of one class of vulnerability. The publication of the YAML hole has caused people to search for a) exploit vectors for that hole, and b) similar classes of exploits that are now much more obvious due to the knowledge of the original hole.

I think that to suggest that this bug could not have been found before is wrong, but the reason we're seeing such a cascade is because security almost never happens in a bubble.