Gunther said while Singh was outwardly unfazed, inwardly the incident had hurt him. He said there were tears in Singh's eyes when he asked him what had happened.
"Foxton is better than this," he said.
"He had done nothing to provoke this outburst. On the contrary, his only 'crime' appeared to be that he was from another race and culture."
It wasn't known if the irate customer was a Foxton local or a visitor passing through the busy state highway.
Gunther said the man burst into a "vicious, obscene, racist diatribe" directed at Singh as he was cooking him a meal.
"He said to him 'don't you touch my food with your dirty slimy hands' and then right went off," he said.
Gunther said given the events of Christchurch a few months ago, when 51 people were killed in a racially motivated attack, he couldn't let the comments go unchallenged.
"New Zealand as a whole is growing richer in our diversity each year as immigrants from many different cultures join us," he said.
"The bottom line is that we are a community, not a collection of individuals ... I just want to stand up and be counted. I want to publicly condemn the racist intolerance that was shown on this occasion."
Singh, 40, had lived in New Zealand since 2011. He had lived in Levin for the past five years and was employed as a chef at the Rangoli restuarant, after previously living in Invercargill, Napier and Kāpiti.
He said on the whole he found New Zealand welcoming and had some good friends.
Singh went back to his homeland of India last year and was married to Ranjit Kaur. He hoped she would join him in New Zealand soon.
Gunther said when Singh was up and running it would represent the first Indian food outlet in Foxton. He couldn't wait to taste the menu.