From here

Klang Hokkien Association president Dr Ler Cheng Chye said simple logic would denounce even the remotest possibilty that yee sang was from Singapore.

"The custom of eating yee sang during Chinese New Year belongs to the Cantonese and given that people of this dialect are mostly from Kuala Lumpur, it must have originated from here," Dr Ler.

What kind of Dr is Dr Ler? What kind of logic is that? It takes only 1 person to invent the dish. It takes Singapore to have only 1 Cantonese to have a remote possibility that it is from Singapore. And we have much more than 1 Cantonese. What do he has inside his skull? Jelly?

And, according to mrbrown,

To be accurate, yusheng (raw fish) has always been around, but Lo-Hei was invented by the founders of Red Star restaurant. In Singapore.

Note: yee sang is yusheng in cantonese. Literally it means raw fish. But it's also another name for Lo-Hei.