Maybe I explained it wrong but it's those Wi-Fi hotspots that your Isps set up around big cities. Your phone will automatically connect to them but they don't have working internet so it kills any activity on your phone internet wise. They also will not let you 'forget' the network as well. Sure I can turn off the Wi-Fi on my phone every single time I use the bus on long distances but it's such a stupid loving thing and an unneeded hassle
There should be a setting to specify whether or not you want to automatically connect to open networks
On my Nexus 6 it's "Use open Wi-Fi automatically" under "Configure Wi-Fi"
You can't filter it down to specific networks, but from a security standpoint, automatically connecting to unknown networks isn't something you really want at all.