It's very cool and Singaporean that they even mix in Hokkien in the Mandarin lyrics!
In most of the Chinese language space people treat different Chinese languages as if they're just different pronounciations, I pronounce it like this, you like that, but it's the "same word", but in Singapore people seem more aware of different Chinese cultural contexts and connotations. "Heng ong huat" is a particular phrase that has to be said in Hokkien, as the equivalent words are not an expression in Mandarin (?).
I can't easily find exactly what the words "heng ong huat" mean etymologically, the hits I get online are very superficial and pragmatic and don't even mention the Chinese characters. It's not simply "gung hei faat choi" ("gong xi fa cai") pronounced in Hokkien, that would be "kiong-hí hoat-châi".