Hi there,
WiFi Security you must know: WPS, WPA 2/3 protected, EAP, and Open. The "free" WiFi network you are talking about is password protected most likely using WPA2, which is not open network, however it is not free because normally customers of the venue will receive upon ordering something such as coffee, therefore you still pay to use their service unless somebody else does not share the secret key with you. Usually the waiter will share the password and the network name after your order.
Next is you can perform recon followed by re association attack to force clients connect