Why was Forsyth County, GA so close in the Dem primary?

[𝕭𝖆𝖕𝖙𝖎𝖘𝖙𝖆 𝕸𝖎𝖓𝖔𝖑𝖆]

It's not at all been Republican for centuries, even though before 1964 it had a lot of Republican votes for a county in the Solid South.
But at the same time, before roughly 1970 Forsyth County was a rural place in the mountains where 10000 people lived and (after a racial riot in 1912) everyone was White. It became heavily Republican under Reagan, presumably because all the people moving there were upper-middle-class, religious, White Atlantans interested in a bedroom community. That growth has continued very much in the 21st century, although it is now more diversified (the 2019 estimates put the Indian American population at 9%! That's probably the highest outside of the Bay Area) (remember also that Indian Americans are the wealthiest ethnic group in the USA).

Basically you have a very very wealthy and very Republican county at the edge of the Appalachians. Most of the Southern Whites who live there likely are very religious, hate taxes like hell and love free trade (unlike conservadems) but likely have also the same racial attitudes as conservadems. So the very few White people in Forsyth County who are Democrats might very well have the same voting patterns as Upland South / Appalachia WWC and what not and in fact before being competitive in 2016, it had been a very narrow win for Clinton over Obama in 2008.

(By the way, Forsyth County had a gigantic 16 points swing towards Clinton in the 2016 GE)