While this can be understood if on a home network or close shared connection, the bigger question is how Inno would differentiate on players that might be on larger single IP provisioned connections like hotels, internet cafes, and the like? The guild I joined in beta have some people residing in neighboring states and/or cities close to me. While I do not know where they live, work, or go for social, what would be the chances of Inno detecting I would be on a shared connection versus I would be on a single connection? Possibly disabling my (or their) ability to donate to their GBs (or mine) for the duration until I get out of range? The only way I can think of is being on my own connection (mobile data) and not going on to wi-fi at hotels, eating spots, malls, etc. if I don't want to worry on it; but that will defeat the purpose of going on wi-fi if on a limited plan.
It's not til you're out of range - the restriction lasts weeks at least if it comes up and links the two accounts. But I haven't heard of any false-positives. It's usually couples that get the restriction.
Note that different machines on the same IP can be distinguished (they'll route back through the same IP, but they have the information necessary to keep on going to your device, not to every device sharing that connection (typically I think different ports will map to different devices is how shared IPs work).