If one does a bit of searching on the internet, the general consensus is that non-oxygenated gasoline will yield slightly higher mpg and octane rating, due to it's higher energy content compared to oxygenated gasoline. From what little I've read and vaguely remember from the debates over oxygenating gasoline from 20+ years ago in CA, non-oxygenated gasoline is slightly better for fuel systems and engines in general.
Therefore, it is hard to imagine that two tanks of non-oxygenated gasoline will cause significant knocking that will result in a spun bearing...
But I too like to speculate. I would suggest that sometime in the past the engine was low on oil for a period of time and the result of that is now appearing. Or, the car was driven in a spirited manner while the engine had not yet reached normal operating temperature.
That being said, what kind of "map" are you using? How often do you change your oil? What oil do you use? I'm no expert on diagnosing spun rod-bearings by ear, but statistically speaking, bearings usually "spin" due to a lack of oil and/or excessive friction.
But even I am using assumptions to come to an unconfirmed conclusion. Paul's question is the most important: What diagnostic test or visual inspection has been performed to actually confirm a spun rod bearing?
70 to engine rebuild faster than you can say "poofff!"