Is there a metaphorical meaning for "Oysters" in this context?

Is there a metaphorical meaning for the word "Oysters" in this context? Or is it just a random animal came to his mind. I have no idea how the situation relates to oysters.

When I first came to Ceylon my Tamil friend A. chaffed me about my way of calling him and the rest of the population, whether Tamil or Mahomedan or Cinghalese, all indiscriminately natives, "as if we were so many oysters!" I told this to Ajax, and of course there was nothing for it after that but to call them all oysters !

Adam's Peak to Elephanta (1892)

Solution 1:

Oyster beds frequently are home to huge numbers of oysters (http://www.oyster-restoration.org/wp-content/uploads/2012/07/CoenLuckRestMonitoring.pdf). There used to be many oyster beds around the UK (http://www.bbc.co.uk/news/science-environment-20042050).

...like so many oysters... . The author is writing at a time when oysters were a well known food. Well known too for being extremely plentiful. The author is recalling how, when he first arrived in Ceylon, he was unable to discriminate among the various peoples ("natives") he met. His friend 'chaffed' his British companion for finding so many different people no more distinguishable from each other than oysters.