On the "first" death certificate, Aline, the spouse is also listed as the informant, possibly the provider of the questionable information.
On the "second" death certificate, issued twelve days later, there is a different informant, Donie (perhaps Dovie) Carey. The second death certificate is a different form which does not include a place for the name of the spouse, but it does indicate that Sidney was married.
Perhaps, Donie/Dovie was actually a closer relative of Sidney and knew more about him that Alene?
Also, another clue: in the 1923 Atlanta directory - Sidney is living at 28 Vernon Place (his residence on the first death certificate and where Aline says she is living on the first death certificate) and Aline is living at 4201/2 . Magnolia. There residence line wasn't filled out on the second death certificate.