preflower wouldn't be much of a sign. most, if not all, photoperiod plants will show preflowers eventually in an extended vege phase.
After 8 weeks, pretty safe to say it is a photoperiod. RQS fucked up packagin or the actual process of creating the "auto" seed with contamination or you got some really bad luck.
i don't know if it's 100% or 99.9% type situation with the genetics. It's possible that the only way you get a non-auto from a proper breeding process is due to a mistake, but could also be a slim chance simply due to the combination of alleles that are possible that dictate this trait (like the chances of a white calf being born, rare but inevitable and not special or magical and merely a possibility that can happen), but it should be incredibly rare, either way.