Polls are not based on static methodologies, they learn and adapt. It is hugely unwise to assume those who run them have not learned from errors last time. It is also worth noting that the error last time was largely down to underestimating the number of student/young voters enthused by Corbyn at that time, the very people he has since alientated and let-down by his unpopular Brexit stance and evasive intransigence on the whole subject.
At this point I can’t decide which I think more likely between a shallow Tory majority and another Tory minority government, but I’m prepared to bet the polling is now closer to reality as some very bright analysts will have reacted to the demographic errors made last time and modified their modelling.