Probably a combination of different inputs, like timezone, regional, GPS (if computer supports that) and figuring out public IP. Knowing Microsoft, they'll try their hardest to avoid flagging a computer as within EEA if they possibly could.
For example, I don't think it's realistic to expect a US citizen traveling to a EU country having to follow US regulations and laws, nor the opposite.
So I'm not sure it would apply in this case either, but I'm not even sure what regulation/law made Microsoft add this change to the update in the first place. If we can figure that out, I guess we could figure out the real answer to your question without guessing.