I don't see Trump getting 14% of the black vote, but I think +4 is about right.
In the subdemos within these polls, what is Black vote in GA, 20% of total electorate?, the difference between 7% and 14% is a handful of respondents, make little of it yes.
To be specific (since GA actually records both voter registration and turnout figures by race), the black share of the electorate was:
2008: 30%
2010: 28%
2012: 30%
2014: 29%
Those numbers are probably understated. Landmark expects 32% black in 2016 (though they estimate it was 33.5% in 2012)/
A lot of voters are "unknown" or don't fill in that category. Voter file research indicates it's mostly black/biracial/nonwhite voters
http://www.peachpundit.com/2014/10/03/new-poll-deal-carter-headed-runoff/#comment-389632http://www.peachpundit.com/2014/10/27/dueling-early-voting-data/#comment-392120