That's the nub of it, yes.
That happened a couple of years ago. I got a "one-off unusual result", got called back for a re-test after which they told me everything was fine. I was particularly careful to not modify my regime *one iota* between those two tests - yet the results improved. I suspect they're refining their test procedures to be more sensitive to 'red flags' on the one hand, and shrinking the 'normal range' on the other in order to catch potential health issues at an earlier stage. But I have nothing to go on but my hunches. Hence the appeal for info from anyone who might have inside knowledge of any such recent changes to testing methodology.