I'm surprised - China's recent foreign policy certainly has not endeared it to South East Asian countries, but even before then mainland Chinese were not exactly treated with open arms in Singapore. You probably won't find it said to your face, but xenophobia against foreigners from China and India is definitely not uncommon.

Discrimination against Chinese goes back 500 years.

There are several reasons: Chinese are rich. Nobody likes the rich. Chinese are foreigners. Nobody likes foreigners. Chinese are heretics and infidels. Nobody likes those. Another cause is the, admittedly brilliant, tactic of divide and conquer that Western colonial powers used. Set the natives up against the Chinese merchants instead of white government officials. The Chinese conveniently lacked the firearms and navy guns that the whites had access to.

There have been many downright genocidal riots against the Chinese across the region. The Chinese government was too weak to do anything about it.

That's not the case here - Singapore is majority Chinese. The sentiments you see are more run of the mill xenophobia - Chinese mainlanders are here to take our jobs, they're loud and unhygienic, they can't speak English, their Chinese has a different accent, etc. You won't hear it being said to your face, but these are not uncommon views.

The comment was about mainland Chinese specifically, not ethnic Chinese, who in Singapore form the majority of the population. In countries like Indonesia--where riots like ones you mentioned have taken place--they are a small minority.