Yes, but the point being made was about the 40% of Democrats not being keen on Harris wasn't it?
Guess the point is that if she doesn't appeal to 40% of Democrats she won't appeal to the undecided % of the population. Fair enough if so.
Polling is very tricky when you have a certaintly on one side - in this case Trump as republican candidate, but a serious of layered hypotheticals on the other - will Biden stand (obviously that has now been resolved), if he doesn't stand who from the Dem side might stand etc etc.
So you may get Dems who, in that hypothetical scenario, may seem luke warm about Harris because they'd prefer Biden or because if not Biden then they'd want someone other than Harris. But once those hypotheticals are resolved - in this case if Harris became the candidate, then they may comfortably prefer Harris to Trump. So it can be really quite difficult to get an accurate picture of opinion until there is the same level of certainty on both sides.