The error rate is given per bit, not per second, i.e. every few bars represents a distinct DRAM chip. That makes some sense, and the article explains quite well why DRAM would behave like that... but I agree that I had to read the article at least twice to figure out that the x-axis on the graph represents the lower bit of the address line!
Still, it's nice to have at least some modern data; https://www.usenix.org/legacy/event/sec08/tech/full_papers/h... is awesome and has much more extensive measurements, but machines from 2007 are somewhat less relevant today.