All right. Turns out, it is a greeting, after all! Perhaps quintessential AusE (Australia & New Zealand).
Jim Nicolson, Long Creek, 2010, p.145 (GoogleBooks) (emphasis added)
(From the Preface): The principal settings are two cattle runs (ranches) in Australia's Northern Territory … In 1947, Darwin's population was 2,538 …
"G'day, Murranji," he called out. "I thought you were still over at the River." "Yeah? How're you going, young feller?" "Good."
"No way Jack'd miss the races and a chance to catch up with old mates. How're you going, Jack?" Brian called out. "Not bad. An' how're yer drinkin', fellers? Left any beer in O'Hara's?"
Ron Player, Under Different Skies, 2010 (GoogleBooks)
(Setting: Narrow Neck Beach, Auckland, New Zealand) Note the
author's remark, "That was a pretty normal greeting in those days."
about "G'day, Allan, how're you going?" (p.24)
Jan Eriksen, Goldmine Experience, 2013 (GoogleBooks)
Di Morrissey, The Islands, 2008, p.535 (GoogleBooks)
D.H. Lawrence, The Primrose Path, in "England, My England":
‘And how’re you going on, lad?’