I've never seen a public WiFi (other than maybe in a very small private cafe) that didn't require some sort of authentication and overt action to connect to it. Either entering a password or clicking through a disclaimer page.

I'm also not sure how push messaging just because you're connected to a WiFi network would work. I'm guessing this was an implementation of Crapple's iBeacon which uses Bluetooth to spam and spy on users. Fortunately easily turned off by disabling Bluetooth.