These lines are descriptive of Gortsby's perception of the elderly gentleman who sits alongside him on the park bench in the "gloaming hour."  Taking a rather cynical point of view regarding the citizenry of the park at dusk, Gortsby perceives the elderly man as having only the last vestiges of self-respect as he no longer can command the esteem of others. While Gortsby sees the old gentleman's clothers are not really shabby, he does not feel that they are at all new:

...but one's imagination could not have pictured the wearer embarking on the purchase of a half-crown box [two shillings, sixpence/35-40 cents] of chocolates or laying out ninepence [20 cents] on a carnation buttonhole

Gortsby does not imagine that the elderly gentleman is affluent enough (20 cents bought quite a bit in the early 1900s) that he can waste money on chocolates or a flower for his coat's button hole.  For, if he were, the gentleman should not be sitting in this park. 

The reader, however, soon learns that Gortsby is not quite the reader of people that he imagines himself.  In fact, the elderly gentleman does return in search of the soap which he has purchased, placing Gortsby in the position of having been taken advantage of by the young man who has come along and taken the elderly gentleman's place and given Gortsby a very tall tale.