Why is the song by Bessie smith described as a 12 bared blues?

Bessie Smith's song "Back Water Blues" is not referred to as a 12-bar blues. It's an eight-bar blues. The 12-bar blues is a traditional blues form consisting of three lines of lyrics for each of the four repeating sections, as well as specific chord progressions and lyrics structure. Bessie Smith's "Back Water Blues," on the other hand, doesn't adhere to this formula.