"Results are weighted to match demographic characteristics, such as race and gender, from the U.S. Census Current Population Survey, and are aligned to the 2012 presidential election outcome using self-reported votes in that election."
This poll gave Hillary a +1 over Trump.
What this means is, they take a poll. Then they change it to match the party affiliations of 2012, which was won by democrats. Republicans didn't show up as much, because Romney was horrific, and democrats turned out above average, because it was fashionable to vote for Obama, and liberals love to be fashionable.
Hillary doesn't have that enthusiasm, she gets minimal crowds (like Romney did) and screwed Bernie Supporters (like Romney did to Paul supporters)
If they were trying to be accurate, they'd have used a multiple election sample to "align" the poll results too, or just use the actual poll results.
I do believe the polls are rigged even beyond this, i.e. take polls more from cities, or more on weekends, things that favor Clinton. This is just the one they admit.
Why are they rigging the polls? Either to depress Trump support or maybe blame Putin for hacking it in hindsight. Or, can they just dial up whatever result they want in the votes? I don't think that is the case, if so they wouldn't be busing people around.
I'm not going to pick one candidates supported platform over the other, but I will say Trump is not a hunchback, evil, murderous, establishment-owned stooge, and he's actually less scandalous sexually than Hillary, but don't expect coverage on that.