While I'm not challenging Mike Scott's answer, I'm curious if that is the actual reason behind your WiFi network working when you got home.

My question is how did you set up the newer phone? If it was just at the store, did the tech do a backup/restore between phones or otherwise transfer any of your old phone's data over to the new one? If that is the case, then WiFi SSID credentials are part of the transfer process and that would explain why your network was joined when you got home.

In addition to Mike Scott's answer, there is another reason why your WiFi network could have been working when you got home.

When the new phone was set up at the store, if the tech did a backup/restore between phones or otherwise transferred any of your old phone's data over to the new one, then settings would have been transferred as well. In this case, WiFi SSID credentials would typically be part of the transfer process and that would explain why your network was joined when you got home.