either it is an auto or it is not.. if changing light hours triggers it, then it's a photoperiod and you better stick to that new scheduel or it'll just revege.
it happens sometimes. either contamination or poor breeding process, or maybe it's just a small percentage chance based on breeding process of autos, i'm not sure. the point is sometimes you'll get a photoperiod.
6weeks isn't the longest vege period for an auto, so there's still plenty of hope. after 8 weeks, i'd start getting concerned, lol. worst case scenario you gotta prune it back a bit and then put it on 12/12 light schedule for 8-10 weeks.