Q: Just lost my iphone6, please help understand.

I lost my iphone6 about 18 hours ago and have find my iPhone on I believe. It's been indicated as offline since as it was switched off immediately. I understand that I will get a message with location when turned on and connected to Internet. How will they connect to Internet wifi when in the area it was stolen I had no known wifi networks that would connect automatically and my mobile data was turned off? When turned on before they can access "settings" to select a network they need my 6 digit passcode, so how will they go to internet, any logic explanation please. Also it doesn't indicate where last it was connected to wifi before being stolen. Thank you in advance.