That, and 50% of the machines where their heuristics say it is a hardware error fail basic memory tests.
I've seen a lot of confirmed bitflips with ECC systems. The vast majority of machines that are impacted are impacted by single event upsets (not reproducible).
(I worded that precisely but strangely because if one machine has a reproducible problem, it might hit it a billion times a second. That means you can't count by "number of corruptions".)
My take is that their 10% estimate is a lower bound.
He doesn't explain anything indeed but presumably that code is available somewhere.