Everybody was involved in earnest discussion - in English. English Corners are a feature of Chinese life everywhere from university campuses to public parks. If a Chinese person is looking to brush up his or her English, these meetings provide an opportunity, free. My chance encounter gave me a chance to observe the crumbling of taboos, even when Chinese are in conversation with a stranger.
In a country where nothing truthful can be written about the Tiananmen massacre, seven years ago this week, one might expect students to avoid politics. But these merely insisted they had more pressing concerns.
When I asked a vague question about the "events of June 1989", I expected them to back off like frightened gazelles. Instead, several of the students sought to clarify. "You mean the Tiananmen crackdown?" asked one. Well, yes, though I had not expected them to use the phrase. "The incident of 4 June" is all that is officially permitted. All agreed that a few years ago they would not have discussed Tiananmen with a foreigner, let alone a journalist. In that respect, China has become more open - despite, not because of, its rulers.
And yet, eerily, almost none of the little crowd, in their teens when the killings took place, seemed bothered about the memory of the suppressed demonstrations. Shanghai, too, saw large demonstrations and there was an unknown number of deaths. One otherwise voluble student remained poignantly silent, his face betraying that he was not indifferent, while the others discussed Tiananmen. He pointedly noted, in response to a question about the future of Communism, which I assumed would be rebuffed: "I could answer that question in private but not here."
But such politicisation was the exception. The police, they agreed, had been "very active" ahead of this year's anniversary but most were not bothered by it. "Money's the number one thing," said one. "If I've got a home and a car, why should I worry about politics?"
Still, as one student pointed out, the political ice is not entirely frozen. The students have just chosen non-party members as student representatives: "That's a significant change, it's never happened before."
After the English Corner broke up, one student hurried after me. "I am sorry it has not been possible to speak more openly," he said. "I wanted to tell you: I don't think the Communists can survive. My parents are party members. In a way it makes me sad to talk with them. But China must change."
On the streets of Shanghai, everything is changing. Shanghai, a kind of regional New York before the Second World War, seeks to blaze once more. Nanking Road, the main shopping street, is non-stop neon.
All the students at the English Corner, when asked what they hope to do after graduation, answered: "Business." These, then, are not obvious radicals. And yet, it would be a brave apparatchik who would stake everything on a belief that politics will remain unchanged.
A Chinese expatriate businessman tells the story of how, when he arrived in Shanghai, a taxi driver provided this analysis of the country's problems: "[President] Jiang Zemin hasn't got a head. And [prime minister] Li Peng hasn't got a heart."
You couldn't have said that a few years ago, the passenger remarked. "No," came back the deadpan reply. "Back then, it was a state secret."