In the few commits from Jia Tan that I've seen, the English parses (to me at least) idiomatically as a native speaker from either the US or UK, and I did not encounter any signs of Singaporean English. Obviously, this is a very small sample so one cannot read too much into it.
Almost 10% of Singaporeans share the family name Tan. [1]
[1] https://en.wikipedia.org/wiki/File:Singaporean_surnames_by_f...