And, also, this is just one pollster, one that has gotten rather odd results so far in many races, so I would take such polls with a grain of salt, especially since, according to their own numbers, Ojeda is actually leading with 2016 voters, but they were screened out.
That's not what the 2016 voters thing means. That alternative scenario showing Ojeda winning is if the electorate were similar to that that voted in 2016 - i.e. if it were a Presidential year size turnout, with the electorate having the same statistical/demographic characteristics as in 2016.
That does not mean that 2016 voters are screened out. There are many 2016 voters included in the turnout scenario that the poll is projecting. Some are screened out, but that is certainly appropriate for a midterm.
The thing is, WV is (perhaps still) one of the few places where Democrats would/should do
better with lower turnout and/or an older voter base. Maybe the generational turnover is complete there now, but the broader dynamic has been true for quite some time throughout a good swath of Appalachia (including KY, where lower turnout might have beat Bevin; I think Conway did best with 65+ year-olds).