The only way they can tell where you're accessing from is by looking at who the IP address range your connection is on comes from. This is often wrong for mobile devices as they get routed through proxies in data centres or similar places, so can't be relied upon. IP geolocation can be useful, but it certainly isn't foolproof.
Although not such an extreme example, my IP address almost always shows me as being in London, whereas I'm convinced I'm actually currently in Bath. In fact, if I look up, I can see Pulteney bridge!