"Passive scrolling" is when you load up something like Facebook or Instagram, and you mindlessly scroll through your feed. These apps implement infinite scrolling, and every n-th post is actually an ad.
The article doesn't mention it, but I think one of the big drivers of the "death" of click through rates as a metric is brand advertising. Advertisers have started to view digital ads more as a long-term brand-building exercise (where brand exposure is all they want) instead of a short-term sales opportunity (where click-through rate rules).
I think since the 90s, brand exposure is all marketers have cared about for newspaper, radio and TV ads - no one measures any equivalent of CTR for those mediums. It's surprising to me that it took them so long to align their digital marketing strategies to this way of thinking. Perhaps having an easy way to measure a metric (in the form of Google Analytics) is the key driver for the adoption of that metric (rather than the usefulness of the metric itself).