He wasn't contending that a K&N (or any filter for that matter) would cause the engine to blow up. What he said was that used oil analysis have shown higher levels of silicon (ie; dirt) in general with those using K&N air filters. And that higher levels of dirt is not good for the engine.
Think of it this way, add 100ppm (not much really) of silicon in the particulate range of 10~25 Nmm (which a K&N filter WILL let in, BTW), and mix it with the oil film on the cylinder walls. Drive normally and let this abrasive paste work it's wonders on the cylinder walls and piston rings for awhile. I bet we see those same folks coming back in here whining about why their cars are now consuming large amounts of oil. Won't happen overnight like "blowing up the engine"
would, but given a short period of time like a couple oil change intervals and there will be measurable wear.