iPhone How to get rid of Wifi network pop up?

[C DM]

Well, as far as I can see there are only two settings. My previous iPhone 5 on iOS 7 didn't act like this. So unless you are telling me my iPhone 6s under 9.0.2 is supposed to connect to my (unknown) neighbor's networks then I'm either still missing something or there is some bug at play here.

Are all networks unsecured and have essentially random and different names?

 

[raab]

I've never seen a phone, Android or iOS, automatically join a wifi network it doesn't know about with or without a password.

Do you have a Mac and iCloud keychain sync enabled on both your iPhone and Mac? You'll be able to see all known wifi networks under your network preferences..

 

[Ash Pole]

I've never seen a phone, Android or iOS, automatically join a wifi network it doesn't know about with or without a password.

If the names are the same as another network you have joined (like the generic "linksys") this will happen. Just click the arrow next to the network name when connected and choose "forget this network".
He should also go to Settings>General>Reset...Reset Network Settings

 

[raab]

Exactly, the SSID has to known

 

[bransoj]

If you've used a back up from your old iPhone i think it will carry the stored Wifi details from that phone as its been used over the the years and your new phone will have them from the restore when you set it up.

Could you reset network settings to erase all the stored wifi set ups and then start again...yes it will be a bit of pain setting up the few that you want to use again but it would clear out all the stored ones.