But OP said his nose didn't detect the smell of fuel in the sample. On the other hand, if 4.6 is accurate, then the smell should have been easily detected. So while we know Blackstone is usually low on that measurement, it appears Oil Analyzers might be high. Unless OP had asymptomatic Covid and lost his sense of smell without realizing it.I think the reason Blackstone didn't infer any fuel was that 390F was above their 385F "trigger". i also suspect a retest would have given a lower flashpoint.
I've come to the conclusion my nose and a blotter are more accurate at spotting fuel dilution than Blackstone.