They didn't. The last year the US Mint struck coins for another country was 1984 (except for the 1000 Kr Iceland coin for the 500th anniversary of Eric the Red's discovery of North America in 2000) 11 years before this cent was struck Which begs the question how did Singapore cent planchets get into the Philadelphia Mint? OK found the probably answer. The Singapore cents were also copper plated zinc. Most likely also produced by Jarden Zinc and some probably accidentally got mixed in with planchets shipped to Philadelphia.
It's not a Malaysian 1 sen planchet, as those are composed of copper-plated steel. The OP's coin is composed of copper-plated zinc. It's also not a Singapore cent planchet. While those are composed of copper-plated zinc, they are much lighter at 1.24 grams. These wrong planchet Lincoln cents vary quite a bit in weight, falling between 1.5 grams and just over 2 grams. They seem to have a bimodal distribution, with most falling at either 1.7 grams or 2 grams. They mystery remains as to what these planchets were intended for and whether they represent two (or more) unrelated populations.