I would never have expected Fitz to improve his accuracy by such a big margin so far this year. But OP is right - there are ways to improve almost any QB's accuracy. Better protection, as Jess noted, is a big one.
Switching offensive systems (or simply becoming more comfortable in an existing system), i think, is another. Fitz is flourishing in his 2nd year in Gailey's offense. He is a smart QB and can handle the progressions of the spread sets. The passing game seems focused on intermediate routes and short passes to our tailbacks, which suits Fitz, who has struggled with deep ball accuracy.
The better pass protection along with a Gailey offense tailor-made to Fitz's strengths has equated to a huge boost in accuracy and an avalanche of points. I'm on board, but am still curious to see how they perform against a great defense.