① The service (e.g. app) will likely be trying to guess your location from your IP address, with a process called internet geolocation. The IP address will be different for connecting through cellular versus connecting through your home network Wi-Fi (or store/school/business Wi-Fi), as that uses different infrastructure to connect to the internet.
The service (e.g. app) will use a remote database of IP addresses and ‘known’ locations, which may or may not be accurate. Unfortunately, the end user has no influence over which database is used by the service. Also, some IP addresses are from a block that may be used in two or more states. This can cause inaccuracies with geolocation. For home networks, user may ask their ISP to update the ‘external’ IP address lease to a different IP with better geolocation.
② Mobile apps may also request a geolocation from GPS in your smart phone. If granted, this would always be more accurate than the former method. Depending on your settings, you may or may not have allowed this use. iPhone apps would do that step through Apple’s Location Services. Turn Location Services and GPS on or off on your iPhone, iPad, or iPod touch - Apple Support