I have found this, not sure how accurate it is.
Per the Oxford English Dictionary, "bangs" as a term for the fringe of hair lying over the forehead originated in the stables. Horses' tails were sometimes allowed to grow to a certain length, and then were cut off in an even, horizontal trim called a "bangtail." Racehorses were sometimes called bangtails. And Green's Dictionary of Slang suggests "bangtail" actually originated in Scotland, not the US. "Bangtail" was first applied to human hairstyles as early as 1844, but the OED cites the first use of "bang" as 1878. "Bang" meaning "abrupt or sudden" has been used in English since the late 18th century