Only about 60% of all Chinese even have a smartphone. [1] "Everyone" you saw was probably a relatively well-off member of the middle class in a first-tier city. As a tourist, you obviously won't see anyone who can't afford visiting a touristy area. Try looking for a place more than an hour from any public transport and check again whether the people there all use cashless payment.

[1] https://www.statista.com/statistics/257045/smartphone-user-p...